Antibody Drug Conjugate Sacituzumab Govitecan Enables A Sequential TOP1/PARP Inhibitor Cancer Therapy Strategy in Breast Cancer Patients

PURPOSE

The Antibody-Drug Conjugate (ADC) Sacituzumab govitecan (SG) comprises the topoisomerase 1 (TOP1) inhibitor SN-38, coupled to a monoclonal antibody targeting trophoblast cell surface antigen 2 (TROP-2). Poly (ADP-ribose) polymerase (PARP) inhibition may synergize with TOP1 inhibitors and SG, but previous studies combining systemic PARP and TOP1 inhibitors failed due to dose-limiting myelosuppression. Here, we assess proof-of-mechanism and clinical feasibility for SG and talazoparib employing an innovative sequential dosing schedule.

PATIENTS AND METHODS

In vitro models tested pharmacodynamic endpoints, and in a phase 1b clinical trial (NCT04039230) 30 patients with metastatic Triple-Negative Breast Cancer (mTNBC) received SG and talazoparib using a concurrent (N=7) or sequential (N=23) schedule. Outcome measures included safety, tolerability, preliminary efficacy and establishment of a recommended phase 2 dose (RP2D).

RESULTS

We hypothesized that tumor-selective delivery of TOP1i via SG would reduce non-tumor toxicity and create a temporal window, enabling sequential dosing of SG and PARP inhibition. In vitro, sequential SG followed by talazoparib delayed TOP1 cleavage complex clearance, increased DNA damage and promoted apoptosis. In the clinical trial, sequential SG/talazoparib successfully met primary objectives and demonstrated median PFS of 7.6 months without Dose-Limiting Toxicities (DLTs), while concurrent dosing yielded 2.3 months PFS and multiple DLTs including severe myelosuppression.

CONCLUSIONS

While SG dosed concurrently with talazoparib is not tolerated clinically due to an insufficient therapeutic window, sequential dosing of SG then talazoparib proved a viable strategy. These findings support further clinical development of the combination and suggest that ADC-based therapy may facilitate novel, mechanism-based dosing strategies.

Genomic spectrum of actionable alterations in serial cell free DNA (cfDNA) analysis of patients with metastatic breast cancer

We aimed to study the incidence and genomic spectrum of actionable alterations (AA) detected in serial cfDNA collections from patients with metastatic breast cancer (MBC). Patients with MBC who underwent plasma-based cfDNA testing (Guardant360®) between 2015 and 2021 at an academic institution were included. For patients with serial draws, new pathogenic alterations in each draw were classified as actionable alterations (AA) if they met ESCAT I or II criteria of the ESMO Scale for Clinical Actionability of Molecular Targets (ESCAT). A total of 344 patients with hormone receptor-positive (HR+)/HER2-negative (HER2-) MBC, 95 patients with triple-negative (TN) MBC and 42 patients with HER2-positive (HER2 + ) MBC had a baseline (BL) cfDNA draw. Of these, 139 HR+/HER2-, 33 TN and 13 HER2+ patients underwent subsequent cfDNA draws. In the HR+/HER2- cohort, the proportion of patients with new AA decreased from 63% at BL to 27-33% in the 2nd-4th draws (p < 0.0001). While some of the new AA in subsequent draws from patients with HR+/HER2- MBC were new actionable variants in the same genes that were known to be altered in previous draws, 10-24% of patients had new AA in previously unaltered genes. The incidence of new AA also decreased with subsequent draws in the TN and HER2+ cohorts (TN: 25% to 0-9%, HER2 + : 38% to 14-15%). While the incidence of new AA in serial cfDNA decreased with subsequent draws across all MBC subtypes, new alterations with a potential impact on treatment selection continued to emerge, particularly for patients with HR+/HER2- MBC.

Response-guided neoadjuvant sacituzumab govitecan for localized triple-negative breast cancer: results from the NeoSTAR trial

BACKGROUND

Sacituzumab govitecan (SG), a novel antibody-drug conjugate (ADC) targeting TROP2, is approved for pre-treated metastatic triple-negative breast cancer (mTNBC). We conducted an investigator-initiated clinical trial evaluating neoadjuvant (NA) SG (NCT04230109), and report primary results.

PATIENTS AND METHODS

Participants with early-stage TNBC received NA SG for four cycles. The primary objective was to assess pathological complete response (pCR) rate in breast and lymph nodes (ypT0/isN0) to SG. Secondary objectives included overall response rate (ORR), safety, event-free survival (EFS), and predictive biomarkers. A response-guided approach was utilized, and subsequent systemic therapy decisions were at the discretion of the treating physician.

RESULTS

From July 2020 to August 2021, 50 participants were enrolled (median age = 48.5 years; 13 clinical stage I disease, 26 stage II, 11 stage III). Forty-nine (98%) completed four cycles of SG. Overall, the pCR rate with SG alone was 30% [n = 15, 95% confidence interval (CI) 18% to 45%]. The ORR per RECIST V1.1 after SG alone was 64% (n = 32/50, 95% CI 77% to 98%). Higher Ki-67 and tumor-infiltrating lymphocytes (TILs) were predictive of pCR to SG (P = 0.007 for Ki-67 and 0.002 for TILs), while baseline TROP2 expression was not (P = 0.440). Common adverse events were nausea (82%), fatigue (76%), alopecia (76%), neutropenia (44%), and rash (48%). With a median follow-up time of 18.9 months (95% CI 16.3-21.9 months), the 2-year EFS for all participants was 95%. Among participants with a pCR with SG (n = 15), the 2-year EFS was 100%.

CONCLUSIONS

In the first NA trial with an ADC in localized TNBC, SG demonstrated single-agent efficacy and feasibility of response-guided escalation/de-escalation. Further research on optimal duration of SG as well as NA combination strategies, including immunotherapy, are needed.

Meiotic protein SYCP2 confers resistance to DNA-damaging agents through R-loop-mediated DNA repair

Drugs targeting the DNA damage response (DDR) are widely used in cancer therapy, but resistance to these drugs remains a major clinical challenge. Here, we show that SYCP2, a meiotic protein in the synaptonemal complex, is aberrantly and commonly expressed in breast and ovarian cancers and associated with broad resistance to DDR drugs. Mechanistically, SYCP2 enhances the repair of DNA double-strand breaks (DSBs) through transcription-coupled homologous recombination (TC-HR). SYCP2 promotes R-loop formation at DSBs and facilitates RAD51 recruitment independently of BRCA1. SYCP2 loss impairs RAD51 localization, reduces TC-HR, and renders tumors sensitive to PARP and topoisomerase I (TOP1) inhibitors. Furthermore, our studies of two clinical cohorts find that SYCP2 overexpression correlates with breast cancer resistance to antibody-conjugated TOP1 inhibitor and ovarian cancer resistance to platinum treatment. Collectively, our data suggest that SYCP2 confers cancer cell resistance to DNA-damaging agents by stimulating R-loop-mediated DSB repair, offering opportunities to improve DDR therapy.

Optimizing Access to Liquid Biopsy in the Present and Future Cancer Landscape

We discuss a recent manuscript providing recommendations to improve use and access for liquid biopsy in oncology.

Virtual Molecular and Precision Medicine Clinic to Improve Access to Clinical Trials for Patients With Metastatic Breast Cancer: An Academic/Community Collaboration

PURPOSE

There is a demand for improved care delivery surrounding genomic testing and clinical trial enrollment among patients with metastatic breast cancer (MBC). We sought to improve the current process via real-time informal consultation and prescreening assessment for patients with MBC treated by community and academic medical oncologists by implementing a virtual molecular and precision medicine (vMAP) clinic.

METHODS

The vMAP program used a virtual referral system directed to a multidisciplinary team with precision medicine expertise. Providers contacted vMAP regarding patients with MBC, and on receipt of referral, the vMAP team engaged in discussion to identify if further diagnostics were needed (including genomic testing) and to identify potential clinical trials or standard treatment options. Recommendations were then sent to the referring provider within 72 hours. Pre-/postsurveys were issued to network physicians to assess for barriers, clinical trial access, and vMAP referral experience. Program implementation was evaluated with the Squire 2.0 reporting guidelines for quality improvement in health care as a framework.

RESULTS

Eighty-one cases from 22 providers were referred to vMAP over a 26-month period. The average response time to the referring provider with a finalized recommendation was 1.90 ± 1.82 days. A total of 86.4% of cases had clinical trial options on vMAP prescreen, with 40.7% initiating formal screening assessments and 27 patients (33.3%) ultimately enrolling on trials. On resurvey, 92% of survey responses across community oncology referring providers said that they were very likely to use vMAP again.

CONCLUSION

In the initial 2-year period, vMAP demonstrated an efficient means to offer real-time interpretation of genomic testing and identification of clinical trials for patients with MBC, with effective clinical trial enrollment and high rates of referring provider satisfaction.

Regulation of RNA methylation by therapy treatment, promotes tumor survival

Our data previously revealed that chemosurviving cancer cells translate specific genes. Here, we find that the m6A-RNA-methyltransferase, METTL3, increases transiently in chemotherapy-treated breast cancer and leukemic cells in vitro and in vivo. Consistently, m6A increases on RNA from chemo-treated cells, and is needed for chemosurvival. This is regulated by eIF2α phosphorylation and mTOR inhibition upon therapy treatment. METTL3 mRNA purification reveals that eIF3 promotes METTL3 translation that is reduced by mutating a 5'UTR m6A-motif or depleting METTL3. METTL3 increase is transient after therapy treatment, as metabolic enzymes that control methylation and thus m6A levels on METTL3 RNA, are altered over time after therapy. Increased METTL3 reduces proliferation and anti-viral immune response genes, and enhances invasion genes, which promote tumor survival. Consistently, overriding phospho-eIF2α prevents METTL3 elevation, and reduces chemosurvival and immune-cell migration. These data reveal that therapy-induced stress signals transiently upregulate METTL3 translation, to alter gene expression for tumor survival.

A Gene Panel Associated With Abemaciclib Utility in ESR1-Mutated Breast Cancer After Prior Cyclin-Dependent Kinase 4/6-Inhibitor Progression

PURPOSE

For patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (MBC), first-line treatment is endocrine therapy (ET) plus cyclin-dependent kinase 4/6 inhibition (CDK4/6i). After disease progression, which often comes with ESR1 resistance mutations (ESR1-MUT), which therapies to use next and for which patients are open questions. An active area of exploration is treatment with further CDK4/6i, particularly abemaciclib, which has distinct pharmacokinetic and pharmacodynamic properties compared with the other approved CDK4/6 inhibitors, palbociclib and ribociclib. We investigated a gene panel to prognosticate abemaciclib susceptibility in patients with ESR1-MUT MBC after palbociclib progression.

METHODS

We examined a multicenter retrospective cohort of patients with ESR1-MUT MBC who received abemaciclib after disease progression on ET plus palbociclib. We generated a panel of CDK4/6i resistance genes and compared abemaciclib progression-free survival (PFS) in patients without versus with mutations in this panel (CDKi-R[-] v CDKi-R[+]). We studied how ESR1-MUT and CDKi-R mutations affect abemaciclib sensitivity of immortalized breast cancer cells and patient-derived circulating tumor cell lines in culture.

RESULTS

In ESR1-MUT MBC with disease progression on ET plus palbociclib, the median PFS was 7.0 months for CDKi-R(-) (n = 17) versus 3.5 months for CDKi-R(+) (n = 11), with a hazard ratio of 2.8 (P = .03). In vitro, CDKi-R alterations but not ESR1-MUT induced abemaciclib resistance in immortalized breast cancer cells and were associated with resistance in circulating tumor cells.

CONCLUSION

For ESR1-MUT MBC with resistance to ET and palbociclib, PFS on abemaciclib is longer for patients with CDKi-R(-) than CDKi-R(+). Although a small and retrospective data set, this is the first demonstration of a genomic panel associated with abemaciclib sensitivity in the postpalbociclib setting. Future directions include testing and improving this panel in additional data sets, to guide therapy selection for patients with HR+/HER2- MBC.

Abstract 960: Overlapping expression landscape of antibody drug conjugate targets, trophoblast cell surface antigen 2 (Trop-2) & human epidermal growth factor receptor 2 (HER2), in breast cancer

Background Antibody drug conjugates (ADC) are novel drugs linking potent payloads to antibodies targeting antigen-expressing tumors. Sacituzumab govitecan (SG), targeting Trop-2, is approved for metastatic triple negative breast cancer (TNBC); and trastuzumab deruxtecan, targeting HER2, is approved for HER2-positive and HER2-low metastatic breast cancer. To understand the potentially overlapping clinical landscape of Trop-2 and HER2 antigens, we evaluated RNA expression data in breast cancer from The Cancer Genome Atlas (TCGA) project.

Methods TCGA dataset was assessed for Trop-2 and HER2 expression via processed RNA sequencing (RNA-seq) data of the corresponding genes TACSTD2 and ERBB2. Medium/high gene expression was assessed as &gt;100 transcripts per million (TPM). Samples were classified HER2-low per ASCO/CAP guidelines. Gene expression across clinical parameters was assessed via one-way ANOVA.

Results 1076 patients with primary breast cancer were included. The majority (59%) had both high TACSTD2 expression (TACSTD2hi) and high ERBB2 expression (ERBB2hi) (see Table). Median TACSTD2 expression was 572 TPM (IQR 349-666 TPM); median ERBB2 expression was 122 TPM (IQR 73-192 TPM). No significant difference was observed in TACSTD2 or ERBB2 expression among invasive ductal carcinoma, invasive lobular carcinoma, mixed histology, or other (p = 0.07, 0.23). No significant difference in TACSTD2 expression was noted between HER2-low and HER2-negative subtypes (p=0.34).

Conclusions While SG is approved in TNBC, TACSTD2 is expressed across all breast cancer subtypes, including HER2-low, suggesting a broader population may benefit from Trop-2-targeted ADCs. Furthermore, given that over half of breast cancers have high expression of both TACSTD2 and ERBB2, additional studies are needed to understand the optimal sequencing of ADC-based therapies for patients with breast cancer.

Table Patient subsets(HR = hormone receptor) n TACSTD2hi & ERBB2hi TACSTD2hi & ERBB2low TACSTD2low & ERBB2hi TACSTD2low & ERBB2low All 1,076 632 (59%) 394 (36%) 19 (2%) 31 (3%) Histology 843 Invasive ductal carcinoma 507 267 (32%) 215 (25%) 10 (1%) 15 (2%) Invasive lobular carcinoma 130 103 (12%) 24 (3%) 1 (&lt;1%) 2 (&lt;1%) Mixed 91 63 (7%) 24 (3%) 2 (&lt;1%) 2 (&lt;1%) Other 115 65 (8%) 43 (5%) 2 (&lt;1%) 5 (&lt;1%) HER2 Status 345 HR+/HER2-low 254 170 (49%) 77 (22%) 6 (1%) 1 (&lt;1%) TNBC/HER2-low 55 12 (3%) 39 (11%) 1 (&lt;1%) 3 (&lt;1%) HR+/HER2-negative 24 13 (4%) 11 (3%) 0 0 TNBC/HER2-negative 12 1 (&lt;1%) 10 0 1 (&lt;1%)

Citation Format: Arielle J. Medford, Nicholas J. Haradhvala, Neelima Vidula, Rachel Abelman, Laura M. Spring, Leif W. Ellisen, Gad Getz, Aditya Bardia. Overlapping expression landscape of antibody drug conjugate targets, trophoblast cell surface antigen 2 (Trop-2) & human epidermal growth factor receptor 2 (HER2), in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 960.

Revisiting Androgen Receptor Signaling in Breast Cancer

Aberrant estrogen receptor (ER) signaling is central to the pathogenesis of many breast cancers. Like ER, the androgen receptor (AR) is a steroid nuclear receptor that is frequently expressed in breast cancer and has long been considered an attractive therapeutic target. Although androgens were historically employed in the treatment of breast cancer, this strategy has largely fallen out of favor with the advent of modern anti--estrogens, due to virilizing effects from androgens, as well as concerns that androgens could be converted to estrogens to fuel tumor growth. Recent molecular advances, however, including the development of selective androgen receptor modulators, have renewed interest in targeting the AR. Yet androgen signaling in breast cancer remains incompletely understood, and preclinical studies have yielded conflicting and sometimes contradictory evidence regarding the role of AR, resulting in clinical investigations into both AR agonists and antagonists. It is increasingly recognized that AR may very well be context-specific, with divergent actions in ER-positive versus ER-negative disease. Here, we will summarize our current understanding of AR biology and insights from recent investigations into AR-directed therapies in breast cancer.

Mechanisms of Resistance to Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs), with antibodies targeted against specific antigens linked to cytotoxic payloads, offer the opportunity for a more specific delivery of chemotherapy and other bioactive payloads to minimize side effects. First approved in the setting of HER2+ breast cancer, more recent ADCs have been developed for triple-negative breast cancer (TNBC) and, most recently, hormone receptor-positive (HR+) breast cancer. While antibody-drug conjugates have compared favorably against traditional chemotherapy in some settings, patients eventually progress on these therapies and require a change in treatment. Mechanisms to explain the resistance to ADCs are highly sought after, in hopes of developing next-line treatment options and expanding the therapeutic windows of existing therapies. These resistance mechanisms are categorized as follows: change in antigen expression, change in ADC processing and resistance, and efflux of the ADC payload. This paper reviews the recently published literature on these mechanisms as well as potential options to overcome these barriers.

TRK inhibitor in a patient with metastatic triple-negative breast cancer and NTRK fusions identified via cell-free DNA analysis

Tissue-agnostic indications for targeted therapies have expanded options for patients with advanced solid tumors. The Food and Drug Administration approvals of the programmed death-ligand 1 inhibitor pembrolizumab and the TRK inhibitors larotrectinib and entrectinib provide rationale for next-generation sequencing (NGS) in effectively all advanced solid tumor patients given potential for clinical responses even in otherwise refractory disease. As proof of concept, this case report describes a 64-year-old woman with triple-negative breast cancer refractory to multiple lines of therapy, found to have a rare mutation on NGS which led to targeted therapy with meaningful response. She initially presented with metastatic recurrence 5 years after treatment for a localized breast cancer, with rapid progression through four lines of therapy in the metastatic setting, including immunotherapy, antibody-drug conjugate-based therapy, and chemotherapy. Germline genetic testing was normal. Ultimately, NGS evaluation of cell-free DNA via an 83-gene assay (Guardant Health, Inc.) identified two NTRK3 fusions: an ETV6-NTRK3 fusion associated with the rare secretory breast carcinoma, and CRTC3-NTRK3, a novel fusion partner not previously described in breast cancer. Liver biopsy was sent for whole exome sequencing and RNA-seq analysis of tissue (BostonGene, Inc., Boston, MA, USA), which provided orthogonal confirmation of both the ETV6-NTRK3 and CRTC3-NTRK3 fusions. She was started on the TRK inhibitor larotrectinib with a marked clinical and radiographic response after only 2 months of therapy. The patient granted verbal consent to share her clinical story, images, and data in this case report. This case demonstrates the significant potential benefits of NGS testing in advanced cancer and the lessons we may learn from individual patient experiences.

Clinical Implications and Treatment Strategies for ESR1 Fusions in Hormone Receptor-Positive Metastatic Breast Cancer: A Case Series

In hormone receptor-positive metastatic breast cancer (HR+ MBC), endocrine resistance is commonly due to genetic alterations of ESR1, the gene encoding estrogen receptor alpha (ERα). While ESR1 point mutations (ESR1-MUT) cause acquired resistance to aromatase inhibition (AI) through constitutive activation, far less is known about the molecular functions and clinical consequences of ESR1 fusions (ESR1-FUS). This case series discusses 4 patients with HR+ MBC with ESR1-FUS in the context of the existing ESR1-FUS literature. We consider therapeutic strategies and raise the hypothesis that CDK4/6 inhibition (CDK4/6i) may be effective against ESR1-FUS with functional ligand-binding domain swaps. These cases highlight the importance of screening for ESR1-FUS in patients with HR+ MBC while continuing investigation of precision treatments for these genomic rearrangements.

Loss of p53 and genetic evolution in pancreatic cancer: Ordered chaos after the guardian is gone

A recent Nature study delineates a stepwise genomic evolution during pancreatic cancer development, employing an engineered mutant Kras and heterozygous Trp53 mouse model that identifies cells undergoing Trp53 loss of heterozygosity (LOH). Genetic progression post-Trp53 LOH involves clonal deletions, then genome doubling and subsequent accumulation of subclonal gains and amplifications.

Immunogenicity of SARS-CoV-2 vaccines in patients with breast cancer

Purpose

To explore the immunogenicity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines in patients with breast cancer based on type of anticancer treatment.

Methods

Patients with breast cancer had anti-spike antibody concentrations measured ⩾14 days after receiving a full SARS-CoV-2 vaccination series. The primary endpoint was IgA/G/M anti-spike antibody concentration. Multiple regression analysis was used to analyze log₁₀-transformed antibody titer concentrations.

Results

Between 29 April and 20 July 2021, 233 patients with breast cancer were enrolled, of whom 212 were eligible for the current analysis. Patients who received mRNA-1273 (Moderna) had the highest antibody concentrations [geometric mean concentration (GMC) in log₁₀: 3.0 U/mL], compared to patients who received BNT162b2 (Pfizer) (GMC: 2.6 U/mL) (multiple regression adjusted p = 0.013) and Ad26.COV2.S (Johnson & Johnson/Janssen) (GMC: 2.6 U/mL) (p = 0.071). Patients receiving cytotoxic therapy had a significantly lower antibody titer GMC (2.5 U/mL) compared to patients on no therapy or endocrine therapy alone (3.0 U/mL) (p = 0.005). Patients on targeted therapies (GMC: 2.7 U/mL) also had a numerically lower GMC compared to patients not receiving therapy/on endocrine therapy alone, although this result was not significant (p = 0.364). Among patients who received an additional dose of vaccine (n = 31), 28 demonstrated an increased antibody response that ranged from 0.2 to >4.4 U/ mL.

Conclusion

Most patients with breast cancer generate detectable anti-spike antibodies following SARS-CoV-2 vaccination, though systemic treatments and vaccine type impact level of response. Further studies are needed to better understand the clinical implications of different antibody levels, the effectiveness of additional SARS-CoV-2 vaccine doses, and the risk of breakthrough infections among patients with breast cancer.

Deep Learning vs Traditional Breast Cancer Risk Models to Support Risk-Based Mammography Screening

BACKGROUND

Deep learning breast cancer risk models demonstrate improved accuracy compared with traditional risk models but have not been prospectively tested. We compared the accuracy of a deep learning risk score derived from the patient's prior mammogram to traditional risk scores to prospectively identify patients with cancer in a cohort due for screening.

METHODS

We collected data on 119 139 bilateral screening mammograms in 57 617 consecutive patients screened at 5 facilities between September 18, 2017, and February 1, 2021. Patient demographics were retrieved from electronic medical records, cancer outcomes determined through regional tumor registry linkage, and comparisons made across risk models using Wilcoxon and Pearson χ2 2-sided tests. Deep learning, Tyrer-Cuzick, and National Cancer Institute Breast Cancer Risk Assessment Tool (NCI BCRAT) risk models were compared with respect to performance metrics and area under the receiver operating characteristic curves.

RESULTS

Cancers detected per thousand patients screened were higher in patients at increased risk by the deep learning model (8.6, 95% confidence interval [CI] = 7.9 to 9.4) compared with Tyrer-Cuzick (4.4, 95% CI = 3.9 to 4.9) and NCI BCRAT (3.8, 95% CI = 3.3 to 4.3) models (P &lt; .001). Area under the receiver operating characteristic curves of the deep learning model (0.68, 95% CI = 0.66 to 0.70) was higher compared with Tyrer-Cuzick (0.57, 95% CI = 0.54 to 0.60) and NCI BCRAT (0.57, 95% CI = 0.54 to 0.60) models. Simulated screening of the top 50th percentile risk by the deep learning model captured statistically significantly more patients with cancer compared with Tyrer-Cuzick and NCI BCRAT models (P &lt; .001).

CONCLUSIONS

A deep learning model to assess breast cancer risk can support feasible and effective risk-based screening and is superior to traditional models to identify patients destined to develop cancer in large screening cohorts.

Abstract 5248: CDK4/6 inhibition (CDK4/6i) is effective in the real-world setting for hormone receptor-positive metastatic breast cancer (HR+ MBC) with ESR1 mutations and fusions

Background For HR+ MBC, ESR1 point mutations (ESR1-MUT) are a common mechanism of acquired resistance to aromatase inhibition (AI); ESR1 fusions (ESR1-FUS) are rare and promote intrinsic resistance to ER-targeting drugs. Retrospective analyses of CDK4/6i trials suggest ESR1-MUT does not cause CDK4/6i resistance, but whether CDK4/6i is effective for ESR1-MUT, or for ESR1-FUS, in the real-world setting is unknown.

Methods Real-world evidence was sourced from the GuardantInform database of commercial payer claims and ctDNA tests from 170,000+ individuals. Patients with MBC who started CDK4/6i within 30 days of ctDNA testing were categorized as ESR1-MUT vs. ESR1-WT and analyzed for time-to-next-treatment (TTNT). Separately, cases with ESR1-FUS detected by tissue RNA-Seq were extracted from a clinicopathologic database at an academic cancer center.

Results There was no significant difference in TTNT on CDK4/6i for ESR1-MUT vs. ESR1-WT. As expected, ESR1-MUT had shorter overall survival (OS), even after adjustment for age, CDK4/6i drug, and prior treatment (HR 0.58 (0.42-0.82), p=0.002, multivariable Cox). Endocrine partner analysis was limited by lack of clinical annotation to 27% of cases: AI was given to 55% of ESR1-WT and 25% of ESR1-MUT; fulvestrant was given to 39% of ESR1-WT and 68% of ESR1-MUT. Additional stratified analyses will be presented.

In the clinicopathologic database, we identified 4 ESR1-FUS cases, and all received CDK4/6i. Progression-free survival durations on CDK4/6i were 4, 10, 11, and 33+ months.

Conclusions Using real-world evidence, we demonstrate that CDK4/6i is effective in both ESR1-MUT and ESR1-WT HR+ MBC, supporting the use of CDK4/6i in this setting. CDK4/6i may be additionally beneficial for patients with ESR1-FUS. Future directions include expanding the ESR1-FUS cohort and deciphering the heterogeneity of CDK4/6i responses in this patient population.

ESR1-WT ESR1-MUT p-value n=612 n=145 TTNT, median days (95% CI) 99 (85-121) 102 (85-152) 0.84 (log-rank) OS, median years (95% CI) 5.1 (4.5-NA) 2.2 (2.0-NA) &lt;0.0001 (log-rank) CDK4/6i drug palbociclib: 71.1% ribociclib: 9.8% abemaciclib: 19.1% palbociclib: 60% ribociclib: 5.5% abemaciclib: 34.5% 0.038 (chi-square) Prior lines of treatment 0: 21.2% 1: 26.1% 2: 18.6% 3+: 34.0% median: 2 0: 15.9% 1: 22.8% 2: 17.2% 3+: 44.1% median: 2 0.013 (Mann-Whitney U)

Citation Format: Jamie O. Brett, Caroline M. Weipert, Lauren L. Ritterhouse, Nicole Zhang, Junhua Yu, Lianne Y. Ryan, Laura M. Spring, Miguel N. Rivera, Jochen K. Lennerz, Dora Dias-Santagata, Leif W. Ellisen, Aditya Bardia, Seth A. Wander. CDK4/6 inhibition (CDK4/6i) is effective in the real-world setting for hormone receptor-positive metastatic breast cancer (HR+ MBC) with ESR1 mutations and fusions [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5248.

Phase 2 study of response-guided neoadjuvant sacituzumab govitecan (IMMU-132) in patients with localized triple-negative breast cancer: Results from the NeoSTAR trial

512

Background: Sacituzumab govitecan (SG), a novel antibody-drug conjugate in which the topoisomerase 1 inhibitor SN-38 (active metabolite of irinotecan) is linked to a humanized monoclonal antibody targeting the tumor antigen Trop2, is currently approved for treatment of patients (pts) with pre-treated metastatic triple negative breast cancer (TNBC). We conducted a phase 2 study evaluating neoadjuvant (NA) SG as upfront therapy for pts with localized TNBC (NCT04230109). The primary objective was to assess pathological complete response (pCR) rate in breast and lymph nodes (ypT0/isN0) with SG. Secondary objectives included assessment of radiological response rate, evaluation of the safety and tolerability (CTCAE v5.0) and event-free survival (EFS). Methods: Patients with localized TNBC (tumor size ≥1cm, or any size if node positive) with no prior treatment were eligible. SG was administered IV on Days 1, 8 of each 21-day cycle at a starting dose of 10 mg/kg for 4 cycles. After 4 cycles, patients with biopsy-proven residual disease, considered as no pCR for primary endpoint, had the option to receive additional NA therapy at the discretion of the treating physician. Radiologic response (US or MRI) was defined by RECIST version 1.1 using a composite response of CR & PR. Standard descriptive statistics were utilized, including 95% binomial confidence intervals for all rates estimated. Results: From 7/14/20 – 8/31/21, 50 pts were enrolled (median age = 48.5; 11 stage I disease, 24 stage II, 11 stage III, 4 unknown; 62% node negative). The majority (98%; n = 49) of pts completed 4 cycles of SG. Overall, the radiological response rate with SG alone was 62% (n = 31, 95% CI 48%, 77%). 26 pts proceeded directly to surgery after SG. Overall, the pCR rate with SG alone was 30% (n = 15/50, 95% CI 18%, 45%). The other 11 pts had RCB-1 (n = 3), RCB-2 (n = 5), and RCB-3 (n = 3) disease, respectively. Of the 24 pts who received additional NA therapy, 6 had a pCR (3 received anthracycline-based regimen, 2 carboplatin/taxane, and 1 docetaxel/cyclophosphamide). Among pts with a germline BRCA mutation (n = 8), 7 proceeded directly to surgery after SG and 6 had a pCR (86%, 95% CI 42%, 99%). The most common AEs with SG were nausea (82%, n = 41), fatigue (78%, n = 39), alopecia (76%, n = 38), neutropenia (58%, n = 29), anemia (36%, n = 18), and rash (48%, n = 24). 6% of pts required dose-reduction. No pts discontinued SG therapy due to disease progression or AEs; 1 discontinued due to minimal response per investigator preference. At the time of data cut-off (1/18/22), no pts experienced disease recurrence. Updated biomarker and EFS results will be presented at the meeting. Conclusions: In the first neoadjuvant trial in TNBC with an ADC, SG demonstrated single agent efficacy in localized TNBC. Further research on optimal duration of SG as well as NA combination strategies, including immunotherapy, are needed. Clinical trial information: NCT04230109.

Utilizing Natural Language Processing (NLP) to identify breast cancer associated-lung metastases from pathology reports to delineate characteristics and challenges of this common site of breast cancer recurrence

e13592

Background: NLP (artificial intelligence) can automate the identification of records in large datasets. The purpose of this study was to evaluate the feasibility of NLP to identify breast cancer-associated lung metastases to understand clinical characteristics and challenges posed by this common site of breast cancer recurrence. Methods: Patients with pathologically confirmed breast cancer associated-lung metastases seen at a large academic center between 3/2012-5/2019 were identified using NLP of institutional pathology reports, with an IRB approved protocol. Chart review was performed to confirm breast cancer associated-lung metastases and determine clinical and pathological features. Results: Using NLP, 32 patients with pathology reports denoting breast cancer associated-lung metastases were identified, with pathologic confirmation of lung biopsy tissue in the majority of cases (24), and pleural fluid specimens (8) on the remainder. Ten of 32 (31%) were HR+/HER2-, 3/32 (9.3%) HER2+, and 19/32 (59%) TNBC. The majority were invasive ductal carcinoma (21/26) with the remainder invasive lobular carcinoma (2/26) or mixed histology (3/26). Median age at lung metastasis diagnosis was 62 years (range 31-88). The median time to development of lung metastasis following primary breast cancer was 5.6 years (range 0-24.8 years). Fifty six percent of lung metastases were detected on imaging and 44% by symptoms including dyspnea, cough, or pain. Tumor tissue genotyping results on the lung metastases were available for 8 patients showing PI3KCA (5), TP53 (3), SMARCA4 (2), ERBB2 (1), FGFR3 (1), ATM (1), CDK4 (1), MYC (1), and ESR1 (1). Treatment after diagnosis of lung metastases included hormone therapy (61%), chemotherapy (84%), lung irradiation (26%), and surgical resection of lung metastases (6%). Lung metastases were associated with considerable morbidity including pleural effusion (15%), dyspnea (6%), pneumothorax (3%), hemothorax (3%), and atelectasis (3%). Patients diagnosed with lung metastases had brain (32%), bone (35%), renal (6%), skin (3%) and adrenal (3%) metastases during disease course. Conclusions: NLP can help identify organ specific metastases from pathology reports, such as breast cancer associated-lung metastases, which can then facilitate observational, translational, and clinical research to characterize and address challenges posed by this common site of breast cancer recurrence. This cohort of patients highlights the morbidity of breast cancer associated-lung metastases and potential role of NLP for disease characterization and clinical research. (Support from ASCO Medical Student Rotation for Underrepresented Populations Award.)

Abstract P1-18-22: AKT inhibition in combination with endocrine therapy and a CDK4/6 inhibitor (CDK4/6i) in patients with hormone receptor positive (HR+)/HER2 negative metastatic breast cancer (MBC) and prior CDK4/6i exposure: A translational investigation

Background: The cyclin-dependent kinase 4/6 inhibitors, with endocrine therapy (ET), have become the standard of care for patients with HR+/HER2- MBC. Prior insight from tumor biopsies and preclinical analyses suggest that AKT1 activation can provoke CDK4/6i resistance, highlighting a potential therapeutic role for AKT inhibition (AKTi) in this setting. However, combinatorial inhibition can be associated with significant toxicity and identification of the optimal biological dose is often challenging. In this translational co-clinical study, we evaluated escalating doses of AKTi combination with CDK 4/6i in parallel patient-derived pre-clinical models as well as a phase 1b clinical trial. Methods: In an open-label phase Ib dose-escalation clinical trial (TAKTIC, NCT03959891), we evaluated the safety, tolerability and efficacy of escalating doses of the AKT1 inhibitor ipatasertib (ipat) in combination with palbociclib (palbo) and fulvestrant (fulv) for patients with HR+/HER2- MBC. Inclusion criteria include unresectable or metastatic disease, at least 1 prior therapy for MBC including any CDK4/6i, and up to 2 prior lines of chemotherapy for MBC (no limit on prior endocrine therapy). In addition, response to escalating doses of ipat and palbo (with fulv) were explored in vitro via an ATP-based viability assay in tumor cell lines derived from circulating tumor cells (CTC) isolated from patients with endocrine-refractory HR+ MBC. Results: In the dose-escalation portion of the phase 1b clinical trial, 23 patients received the triplet combination of ipat, palbo, and fulv (median number of prior lines = 4.3, range 1-7; 100% with prior CDK4/6i): 3 pts received ipat at 200mg + 125mg palbo, 15 pts received 300mg + 125mg palbo, and 5 pts received 400mg + 100mg palbo, all with fulv (500 mg). Among the 23 patients, 20 patients (86.9%) had disease control (4 partial response and 16 stable disease) as the best response, per RECIST. Grade 3/4 toxicities included neutropenia (n=20), lymphopenia (n=3), diarrhea (n=3), thrombocytopenia (n=2), transaminitis (n=2), and rash (n=2). Two DLTs were observed in the 300mg ipat + 125mg palbo cohort (grade 4 neutropenia ≥ 7 days), but none at 400mg + 100mg palbo. The combination of ipat and palbo demonstrated an additive effect in vitro, with increased sensitivity to lower doses of palbo in the presence of ipat. Based on the totality of data, 400mg ipat + 100mg palbo + fulv 500 mg was selected as the recommended phase II dose (RP2D) in the post-CDK4/6i setting. Conclusions: The triplet combination of endocrine therapy with AKTi and lower dose CDK4/6i appears to be well tolerated in heavily pre-treated pts, with preliminary evidence of clinical activity. Further study is needed to evaluate biomarkers associated with higher AKTi benefit in order to guide rational development of combination therapy for patients with HR+/HER2- MBC in the post-CDK4/6i setting. Overall, this translational study demonstrates how insight into the molecular mechanisms of CDK4/6i resistance and combinatorial modeling can be leveraged to develop actionable therapeutic regimens for patients with MBC.

Citation Format: Seth A. Wander, Douglas S. Micalizzi, Taronish Dubash, Dejan Juric, Laura M. Spring, Neelima Vidula, Jennifer Keenan, Maureen Beeler, Elene Viscosi, Dante Che, Elizabeth L. Fisher, Rachel A. Hepp, Beverly Moy, Steven J. Isakoff, Leif W. Ellisen, Jeffrey G. Supko, Shyamala Maheswaran, Daniel A. Haber, Aditya Bardia. AKT inhibition in combination with endocrine therapy and a CDK4/6 inhibitor (CDK4/6i) in patients with hormone receptor positive (HR+)/HER2 negative metastatic breast cancer (MBC) and prior CDK4/6i exposure: A translational investigation [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-18-22.

Abstract P3-23-02: Immunogenicity of SARS-CoV-2 vaccines in patients with breast cancer receiving CDK 4/6 inhibitors

Background: CDK 4/6 inhibitors have transformed the landscape of breast oncology. A CDK 4/6 inhibitor in combination with endocrine therapy is recommended as 1st line therapy for patients with metastatic hormone receptor positive breast cancer. CDK 4/6 inhibitors have purported immunomodulatory effects and while effective, myelosuppression is a common adverse effect of CDK 4/6 inhibitor treatment of breast cancer. The impact of CDK 4/6 inhibitor therapy on immunogenicity of vaccines is not known. In this study, we evaluated the spike antibody response to SARS-CoV-2 vaccines among patients with breast cancer receiving endocrine therapy with or without CDK 4/6 inhibitors.Methods: In the Cancer COVID and Vaccine (CANVAX) study eligible patients included patients with breast cancer who had completed all scheduled doses of SARS-CoV-2 vaccines. Chart review was conducted to identify patients who had received endocrine therapy with or without CDK 4/6 inhibitor. We used validated assays to measure anti-SARS-CoV-2 total IgA/M/G spike antibodies and virus neutralization. We evaluated the magnitude of antibody response based on geometric mean concentrations (GMCs) as well as the % of patients with inadequate seroconversion (defined as levels &lt;100 U/ml). Independent T-test based on log-transformed antibody values was utilized to compare the spike antibody levels and p value of ≤ 0.05 was considered statistically significant.Results: Between April 2021 and June 2021, 203 patients with breast cancer were enrolled. As of the cut-off date (2nd July 2021), results were available for 73 patients treated with endocrine therapy alone (N = 23), or with CDK 4/6 inhibitor-based therapy (N = 50). Most were females (98.6%), white (83.6%), and had metastatic breast cancer (68.5%). 49.3% had received BNT162b2 (Pfizer), 37% mRNA1273 (Moderna), and 13.7% Ad26.COV2.S (Johnson and Johnson/Janssen) vaccines. Overall, the mean spike antibody levels were similar between patients treated with endocrine therapy alone vs CDK 4/6 inhibitor-based therapy (GMC: 326 vs. 719 U/mL; p=0.704). Mean spike antibody levels were higher in patients with early breast cancer vs. metastatic breast cancer (GMC: 555 vs. 465 U/mL; p=0.031). However, patients who received Ad26.COV2.S had lower levels of mean spike antibody levels (GMC 47 U/ml), compared with patients treated with BNT162b2 (GMC 400 U/ml) or mRNA1273 (GMC 2203 U/mL; P&lt;0.01 for both comparisons). Comparison of neutralization titers in 66 individuals supported the above results. 11 (15.1%) patients had low antibody titers (&lt;100U/ml) of seroconversion and 3 received a booster vaccine, with 1 having available repeat titer results thus far demonstrating a significant improvement.Conclusions: The majority of patients receiving CDK 4/6 inhibitor have adequate antibody response to SARS-CoV-2 vaccines, particularly mRNA vaccines. However, a minority of patients may require booster vaccine to augment immunity. Monitoring spike antibody levels could be helpful to identify patients with inadequate seroconversion and guide mitigation strategies for patients with breast cancer.

Citation Format: Elyssa Denault, Erika Nakajima, Vivek Naranbhai, Alejandro Balazs, Lindsey Mortensen, Elizabeth Niehoff, Caroline Barabell, Jennifer A. Hutchinson, Seth A. Wander, Aron S. Rosenstock, Leif W. Ellisen, Beverly Moy, Steven J. Isakoff, Justin F. Gainor, A. John Iafrate, Aditya Bardia, Laura M. Spring. Immunogenicity of SARS-CoV-2 vaccines in patients with breast cancer receiving CDK 4/6 inhibitors [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-23-02.

Abstract OT2-24-03: Phase II study of a PARP inhibitor in metastatic breast cancer with somaticBRCA1/2mutations identified by cell-free DNA: Genotyping based clinical trial

Background: Two PARP inhibitors are approved for germline BRCA1/2 mutant metastatic breast cancer (MBC), based on clinical trials demonstrating an improvement in patient outcomes and quality of life. However, germline BRCA1/2 mutations are identified in 5-10% of breast cancer, limiting their potential applicability. Our prior work demonstrated that somatic BRCA1/2 mutations can be detected in cell-free DNA (cfDNA) in a proportion of patients with MBC who are not germline BRCA1/2 carriers, and that a PARP inhibitor caused growth inhibition in a circulating tumor cell line generated from a patient with MBC and a pathogenic somatic BRCA1 mutation (Vidula, Dubash, CCR, 2020). Thus, we hypothesize that a PARP inhibitor may have efficacy in somatic BRCA1/2 mutant MBC identified by cfDNA. Trial Design: This phase II investigator initiated open label clinical trial is enrolling 30 patients who have pathogenic somatic BRCA1/2 mutations found in cfDNA. Patients must not be known germline BRCA1/2 carriers. Patients receive treatment with the PARP inhibitor, talazoparib, until disease progression. Serial imaging (CT chest, abdomen, pelvis, and bone scan) occurs every 3 months, and cfDNA is collected monthly to evaluate changes in the genomic environment. Patients will also have blood collected at baseline for the Cancer Risk B assay (CR-B), a novel flow variant assay to assess double strand break repair mutations in circulating blood cells (Syeda, Genetics, 2017). Eligibility criteria: Patients with MBC (TNBC with ≥ 1 prior chemotherapy or HR+/HER2- with ≥ 1 prior hormone therapy or ineligible for hormone therapy) with a somatic BRCA1/2 mutation identified in cfDNA (established pathogenic variant) are being enrolled. Patients should not be known germline BRCA1/2 carriers (genetic testing is not required but can be obtained per physician discretion) and may not have previously received a PARP inhibitor. There is no limit on the number of prior therapies, and a prior platinum chemotherapy is allowed in the absence of disease progression on the platinum. Patients must have adequate performance status and organ function. Specific Aims: The primary endpoint is progression-free survival (PFS) using RECIST 1.1. Secondary endpoints include objective response rate and toxicity (NCI CTCAE v 5.0). Exploratory objectives include evaluating serial changes in BRCA1/2 mutant allelic frequency in cfDNA, evaluating the impact of BRCA1/2 reversion mutations, comparing pre- and post-treatment cfDNA results to identify markers of resistance, evaluating the CR-B assay positivity rate, and ultimately correlating these analyses with treatment response. Statistical Methods: A two-stage design with 80% power to demonstrate that talazoparib is associated with “success” (PFS &gt; 12 weeks) in ≥53% patients (4% alpha) is being used. Accrual: This study (NCT03990896) is currently open at Massachusetts General Hospital, where 4 patients are completing screening for enrollment. This study will be activated soon at the University of California San Francisco, MD Anderson, Mayo Clinic Rochester and Jacksonville, Northwestern, and Emory (7 academic centers). Funding: Support for this study is provided by a Pfizer ASPIRE award and Conquer Cancer Foundation of ASCO–Breast Cancer Research Foundation- Career Development Award. Contact information: Neelima Vidula, MD, Massachusetts General Hospital, nvidula@mgh.harvard.edu

Citation Format: Neelima Vidula, Erica Blouch, Erin Basile, Nathan Royce Ruffle-Deignan, Nora Horick, Senthil Damodaran, Alvaro Moreno Aspitia, Manali Bhave, Ami Shah, Minetta C. Liu, Joseph Sparano, Harry Ostrer, Hope Rugo, Leif W. Ellisen, Aditya Bardia. Phase II study of a PARP inhibitor in metastatic breast cancer with somaticBRCA1/2mutations identified by cell-free DNA: Genotyping based clinical trial [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT2-24-03.

Immune activation and evolution through chemotherapy plus checkpoint blockade in triple-negative breast cancer

Immune checkpoint blockade plus chemotherapy is emerging as a standard treatment for some patients with triple-negative breast cancer (TNBC). In this issue of Cancer Cell, Zhang et al. employ extensive single-cell immune compartment analyses of pre- and post-therapy TNBC, and they reveal potential mechanisms of T cell activation and patterns of immune evolution that may inform future biomarkers of response and clinical benefit.

Phase II trial of veliparib and temozolomide in metastatic breast cancer patients with and without BRCA1/2 mutations

PURPOSE

We evaluated the efficacy and safety of poly-(adenosine diphosphate-ribose) polymerase (PARP) 1 and 2 inhibitor veliparib and temozolomide in metastatic breast cancer patients with and without germline BRCA1/2 mutations.

METHODS

In this single-arm phase II trial, patients with metastatic breast cancer received veliparib 30 to 40 mg twice daily on days 1 to 7 with concurrent temozolomide 150 mg/m² on days 1 to 5 of a 28-day cycle. The primary cohort was unselected for BRCA mutation status, and an expansion cohort enrolled only BRCA1/2 carriers. The primary endpoint was objective response rate (ORR) in each cohort. Secondary endpoints included progression-free survival (PFS), clinical benefit rate (CBR), and evaluation of safety and tolerability.

RESULTS

In the primary cohort of 41 unselected patients, which included 9 BRCA mutation carriers, the ORR was 10% and clinical benefit rate at 4 months (CBR) was 27%. In the expansion cohort of 21 BRCA1/2 carriers, the ORR was 14% and CBR was 43%. Among all 30 BRCA1/2 carriers, the ORR was 23% versus 0% among non-carriers. In the subset of BRCA1/2 carriers, the ORR was 32% among platinum-naïve patients versus 9% among platinum-exposed patients. The median PFS was 3.3 months among BRCA1/2 carriers compared to 1.8 months among non-carriers (HR: 0.48, p = 0.006). A longer median PFS of 6.2 months was observed among BRCA1/2 carriers who had no prior platinum therapy. The most common grade 3 and 4 toxicities were thrombocytopenia (32%) and neutropenia (21%) that generally improved with dose modifications.

CONCLUSION

Veliparib and temozolomide demonstrated clinical activity in platinum-naïve BRCA-associated metastatic breast cancer with manageable toxicity at doses of veliparib well below the single-agent active dose. Although the study did not meet its primary endpoint in unselected nor BRCA-associated breast cancer, this regimen was further evaluated in the BROCADE 2 study.

TRIAL REGISTRATION

NCT01009788 (ClinicalTrials.gov), November 9, 2009.

Systematic tissue collection during clinical breast biopsy is feasible, safe and enables high-content translational analyses

Systematic collection of fresh tissues for research at the time of diagnostic image-guided breast biopsy has the potential to fuel a wide variety of innovative studies. Here we report the initial experience, including safety, feasibility, and laboratory proof-of-principle, with the collection and analysis of research specimens obtained via breast core needle biopsy immediately following routine clinical biopsy at a single institution over a 14-month period. Patients underwent one or two additional core biopsies following collection of all necessary clinical specimens. In total, 395 patients were approached and 270 consented to the research study, yielding a 68.4% consent rate. Among consenting patients, 238 lesions were biopsied for research, resulting in 446 research specimens collected. No immediate complications were observed. Representative research core specimens showed high diagnostic concordance with clinical core biopsies. Flow cytometry demonstrated consistent recovery of hundreds to thousands of viable cells per research core. Among a group of HER2 + tumor research specimens, HER2 assessment by flow cytometry correlated highly with immunohistochemistry (IHC) staining, and in addition revealed extensive inter- and intra-tumoral variation in HER2 levels of potential clinical relevance. Suitability for single-cell transcriptomic analysis was demonstrated for a triple-negative tumor core biopsy, revealing substantial cellular diversity in the tumor immune microenvironment, including a prognostically relevant T cell subpopulation. Thus, collection of fresh tissues for research purposes at the time of diagnostic breast biopsy is safe, feasible and efficient, and may provide a high-yield mechanism to generate a rich tissue repository for a wide variety of cross-disciplinary research.

Parallel Genomic Alterations of Antigen and Payload Targets Mediate Polyclonal Acquired Clinical Resistance to Sacituzumab Govitecan in Triple-Negative Breast Cancer

Sacituzumab govitecan (SG), the first antibody-drug conjugate (ADC) approved for triple-negative breast cancer, incorporates the anti-TROP2 antibody hRS7 conjugated to a topoisomerase-1 (TOP1) inhibitor payload. We sought to identify mechanisms of SG resistance through RNA and whole-exome sequencing of pretreatment and postprogression specimens. One patient exhibiting de novo progression lacked TROP2 expression, in contrast to robust TROP2 expression and focal genomic amplification of TACSTD2/TROP2 observed in a patient with a deep, prolonged response to SG. Analysis of acquired genomic resistance in this case revealed one phylogenetic branch harboring a canonical TOP1 ^E418K resistance mutation and subsequent frameshift TOP1 mutation, whereas a distinct branch exhibited a novel TACSTD2/TROP2 ^T256R missense mutation. Reconstitution experiments demonstrated that TROP2^T256R confers SG resistance via defective plasma membrane localization and reduced cell-surface binding by hRS7. These findings highlight parallel genomic alterations in both antibody and payload targets associated with resistance to SG. SIGNIFICANCE: These findings underscore TROP2 as a response determinant and reveal acquired SG resistance mechanisms involving the direct antibody and drug payload targets in distinct metastatic subclones of an individual patient. This study highlights the specificity of SG and illustrates how such mechanisms will inform therapeutic strategies to overcome ADC resistance.This article is highlighted in the In This Issue feature, p. 2355.

Locally Recurrent Secretory Carcinoma of the Breast with NTRK3 Gene Fusion

Enhanced understanding of the molecular events underlying oncogenesis has led to the development of "tumor-agnostic" treatment strategies, which aim to target a tumor's genomic profile regardless of its anatomic site of origin. A classic example is the translocation resulting in an ETV6-NTRK3 gene fusion, a characteristic driver of a histologically diverse array of cancers. The chimeric ETV6-NTRK3 fusion protein elicits constitutive activation of the tropomyosin receptor kinase (TRK) C protein, leading to increased cell survival, growth, and proliferation. Two TRK inhibitors, larotrectinib and entrectinib, are currently approved for use in the metastatic setting for the treatment of advanced solid tumors harboring NTRK fusions. Here we report a rare case of recurrent secretory carcinoma of the breast (SCB) with NTRK3 gene fusion. Whereas most cases of SCB represent slow-growing tumors with favorable outcomes, the case detailed here is the first to the authors' knowledge of recurrence within 1 year of surgery. We review the molecular findings and potential clinical significance. KEY POINTS: The translocation resulting in the ETV6-NTRK3 gene fusion is a known oncogenic driver characteristic of secretory carcinoma of the breast (SCB). Whereas most cases of SCB represent slow-growing tumors with favorable outcomes, the case here with ETV6-NTRK3 gene fusion had local recurrence within 1 year of surgery. Two tropomyosin receptor kinase (TRK) inhibitors, larotrectinib and entrectinib, are approved to treat NTRK fusion-positive tumors, demonstrating sustained high overall response rates in the metastatic setting. Approval of TRK inhibitors necessitates optimization of NTRK fusion detection assays, including detection with liquid biopsies.

RASAL2 Confers Collateral MEK/EGFR Dependency in Chemoresistant Triple-Negative Breast Cancer

PURPOSE

While chemotherapy remains the standard treatment for triple-negative breast cancer (TNBC), identifying and managing chemoresistant tumors has proven elusive. We sought to discover hallmarks and therapeutically actionable features of refractory TNBC through molecular analysis of primary chemoresistant TNBC specimens.

EXPERIMENTAL DESIGN

We performed transcriptional profiling of tumors from a phase II clinical trial of platinum chemotherapy for advanced TNBC (TBCRC-009), revealing a gene expression signature that identified de novo chemorefractory tumors. We then employed pharmacogenomic data mining, proteomic and other molecular studies to define the therapeutic vulnerabilities of these tumors.

RESULTS

We reveal the RAS-GTPase-activating protein (RAS-GAP) RASAL2 as an upregulated factor that mediates chemotherapy resistance but also an exquisite collateral sensitivity to combination MAP kinase kinase (MEK1/2) and EGFR inhibitors in TNBC. Mechanistically, RASAL2 GAP activity is required to confer kinase inhibitor sensitivity, as RASAL2-high TNBCs sustain basal RAS activity through suppression of negative feedback regulators SPRY1/2, together with EGFR upregulation. Consequently, RASAL2 expression results in failed feedback compensation upon co-inhibition of MEK1/2 and EGFR that induces synergistic apoptosis in vitro and in vivo. In patients with TNBC, high RASAL2 levels predict clinical chemotherapy response and long-term outcomes, and are associated via direct transcriptional regulation with activated oncogenic Yes-Associated Protein (YAP). Accordingly, chemorefractory patient-derived TNBC models exhibit YAP activation, high RASAL2 expression, and tumor regression in response to MEK/EGFR inhibitor combinations despite well-tolerated intermittent dosing.

CONCLUSIONS

These findings identify RASAL2 as a mediator of TNBC chemoresistance that rewires MAPK feedback and cross-talk to confer profound collateral sensitivity to combination MEK1/2 and EGFR inhibitors.

Tumor Tissue- versus Plasma-based Genotyping for Selection of Matched Therapy and Impact on Clinical Outcomes in Patients with Metastatic Breast Cancer

PURPOSE

Actionable mutations can guide genotype-directed matched therapy. We evaluated the utility of tissue-based and plasma-based genotyping for the identification of actionable mutations and selection of matched therapy in patients with metastatic breast cancer (MBC).

EXPERIMENTAL DESIGN

Patients with MBC who underwent tissue genotyping (institutional platform, 91-gene assay) or plasma-based cell-free DNA (cfDNA, Guardant360, 73-gene assay) between January 2016 and December 2017 were included. A chart review of records to identify subtype, demographics, treatment, outcomes, and tissue genotyping or cfDNA results was performed. The incidence of actionable mutations and the selection of matched therapy in tissue genotyping or cfDNA cohorts was determined. The impact of matched therapy status on overall survival (OS) in tissue genotyping or cfDNA subgroups was determined with Cox regression analysis.

RESULTS

Of 252 patients who underwent cfDNA testing, 232 (92%) had detectable mutations, 196 (78%) had actionable mutations, and 86 (34%) received matched therapy. Of 118 patients who underwent tissue genotyping, 90 (76%) had detectable mutations, 59 (50%) had actionable mutations, and 13 (11%) received matched therapy. For cfDNA patients with actionable mutations, matched versus nonmatched therapy was associated with better OS [HR 0.41, 95% confidence interval (CI): 0.23-0.73, P = 0.002], and this remained significant in a multivariable analysis correcting for age, subtype, visceral metastases, and brain metastases (HR = 0.46, 95% CI: 0.26-0.83, P = 0.010).

CONCLUSIONS

Plasma-based genotyping identified high rates of actionable mutations, which was associated with significant application of matched therapy and better OS in patients with MBC.See related commentary by Rugo and Huppert, p. 3275.

Twenty-one-gene recurrence score (RS) in germline (g)CHEK2 mutation-associated versus sporadic breast cancers (BC): A multi-site case-control study

10531

Background: Genomic assays, such as RS, are used to determine chemotherapy benefit in early-stage, estrogen receptor (ER)- and/or progesterone receptor (PR)-positive, HER2 negative BC patients (pts). Currently, guidelines to use pts’ germline genetic testing results to guide adjuvant therapy are lacking. Several reports have indicated worse outcomes for BC pts with g CHEK2 pathogenic variants (PV). We investigated whether PV in CHEK2 were associated with increased RS. Methods: Patient-level clinical data and RS were derived from electronic medical records of seven medical centers between years 2013-17. Confirmation of RS using the Genomic Health provider portal was performed. 38 pts with germline PV in CHEK2 (15 pts/39.5% with c.1100delC mutation) and RS score (cases) were matched with BC pts whose genetic testing did not identify PV (controls) using a 1:2 matching schema. Pts were matched based on age at diagnosis and lymph node (LN) status. LN negative pts were further matched based on T-stage. A multivariate random intercept linear mixed model of CHEK2 mutation status on RS was performed, adjusting for PR. A secondary ordinal univariate analysis was conducted that categorized RS into low, intermediate and high risk ( < 18, 18-30, and > 30, respectively). P-values were reported based on a null hypothesis of no effect against a two-sided alternative. Results: The median RS for cases was 19.5 (interquartile range [IQR]: 15 to 25) and the median RS for controls was 18 (IQR: 12 to 22). A greater proportion of cases were categorized as high risk (10.5%) compared to controls (5.6%), and a smaller proportion of cases were categorized as low risk (36.8%) compared to controls (49.3%). Cases had higher grade and increased proportion of PR-negative BC as compared with controls (grade 1: 12.1% of cases versus 32.4% of controls; PR-negative: 7.9% of cases versus 5.6% of controls). The variables used to match cases and controls (age, lymph node status, and T-stage) had similar summary statistics. The RS was 1.97-point higher in pts with g CHEK2 PV compared to controls, after adjusting for PR (95% confidence interval [CI]: 1.02-point lower to 4.96-point higher; p = 0.194). The secondary analysis of CHEK2 mutation status on an ordinal RS risk group yielded comparable results; on average, the odds of being high risk compared to the combined intermediate/low risk groups was 1.72 times higher in cases compared to controls (95% CI: 0.77 to 3.80; p = 0.181), but these differences were not significant. Conclusions: Our case-control study did not show a statistically higher RS for BC that develops in pts with g CHEK2 PV. Further studies are warranted to evaluate the association between type of CHEK2 PV (frameshift versus missense) and other modifying genetic variables and RS.

Clinical Outcomes With Abemaciclib After Prior CDK4/6 Inhibitor Progression in Breast Cancer: A Multicenter Experience

BACKGROUND

Inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6i) are widely used as first-line therapy for hormone receptor-positive metastatic breast cancer (HR+ MBC). Although abemaciclib monotherapy is also FDA-approved for treatment of disease progression on endocrine therapy, there is limited insight into the clinical activity of abemaciclib after progression on prior CDK4/6i.

PATIENTS AND METHODS

We identified patients with HR+ MBC from 6 cancer centers in the United States who received abemaciclib after disease progression on prior CDK4/6i, and abstracted clinical features, outcomes, toxicity, and predictive biomarkers.

RESULTS

In the multicenter cohort, abemaciclib was well tolerated after a prior course of CDK4/6i (palbociclib)-based therapy; a minority of patients discontinued abemaciclib because of toxicity without progression (9.2%). After progression on palbociclib, most patients (71.3%) received nonsequential therapy with abemaciclib (with ≥1 intervening non-CDK4/6i regimens), with most receiving abemaciclib with an antiestrogen agent (fulvestrant, 47.1%; aromatase inhibitor, 27.6%), and the remainder receiving abemaciclib monotherapy (19.5%). Median progression-free survival for abemaciclib in this population was 5.3 months and median overall survival was 17.2 months, notably similar to results obtained in the MONARCH-1 study of abemaciclib monotherapy in heavily pretreated HR+/HER2-negative CDK4/6i-naïve patients. A total of 36.8% of patients received abemaciclib for ≥6 months. There was no relationship between the duration of clinical benefit while on palbociclib and the subsequent duration of treatment with abemaciclib. RB1, ERBB2, and CCNE1 alterations were noted among patients with rapid progression on abemaciclib.

CONCLUSIONS

A subset of patients with HR+ MBC continue to derive clinical benefit from abemaciclib after progression on prior palbociclib. These results highlight the need for future studies to confirm molecular predictors of cross-resistance to CDK4/6i therapy and to better characterize the utility of abemaciclib after disease progression on prior CDK4/6i.

Abstract OT-30-02: Phase II study of talazoparib, a PARP inhibitor, in somatic BRCA1/2 mutant metastatic breast cancer

Background: PARP inhibitors are currently approved for the treatment of germline BRCA1/2 mutant metastatic breast cancer, and have been shown to improve outcomes and patient quality of life. However, germline BRCA1/2 mutations are observed in 5-10% of breast cancer, limiting the applicability of this well-tolerated therapy. We previously identified that a proportion of patients have somatic BRCA1/2 mutations detected by cell-free DNA (cfDNA), in the absence of germline BRCA1/2 mutations, and have demonstrated that a PARP inhibitor has therapeutic efficacy in a circulating tumor cell-line developed from a patient with a somatic BRCA1 mutation (Vidula, CCR, 2020). We hypothesize that PARP inhibitors may be effective in somatic BRCA1/2 mutant metastatic breast cancer identified via cfDNA.

Trial Design: In this phase II investigator initiated single-arm clinical trial, 30 patients with pathogenic somatic BRCA1/2 mutations detected by cfDNA in the absence of a known germline BRCA1/2 mutation will be treated with talazoparib, a PARP inhibitor, until development of disease progression or unacceptable toxicity. Patients will undergo serial imaging with CT chest, abdomen, and pelvis and bone scan every 12 weeks, and cfDNA collection every 4 weeks.

Eligibility criteria: Patients with metastatic breast cancer that is triple-negative (with receipt of at least 1 prior line of chemotherapy) or hormone receptor positive, HER2 negative (with receipt of at least 1 prior line of hormone therapy or considered inappropriate for hormone therapy) are eligible. Patients must not have received a PARP inhibitor and must not have a germline BRCA1/2 mutation. Any number of prior lines of therapy are allowed. The somatic BRCA1/2 mutation detected in cfDNA must be an established pathogenic variant. Adequate organ function is also required.

Specific Aims: 1. To determine progression-free survival (PFS) by RECIST 1.1 (Primary endpoint), 2. Objective response rate, 3. Safety and tolerability by NCI CTCAE v 5.0, 4. Serial changes in BRCA1/2 mutant allelic frequency in cfDNA, and compare pre- and post-treatment cfDNA results with treatment (Exploratory aim).

Statistical Methods: Patients are being enrolled in a two-stage design, which provides 80% power to demonstrate that the study treatment is associated with “success” (PFS &gt; 12 weeks) in ≥53% patients (4% alpha).

Accrual: Patients are being screened for enrollment at the Massachusetts General Hospital. This study is also opening at other sites in the U.S. including the University of California San Francisco. (NCT03990896)

Funding: This study is funded by Pfizer ASPIRE award and Conquer Cancer Foundation of ASCO Career Development Award. Contact information: Neelima Vidula, MD, Massachusetts General Hospital, nvidula@mgh.harvard.edu

Citation Format: Neelima Vidula, Nora Horick, Erin Basile, Erica Blouch, Leif W. Ellisen, Hope S. Rugo, Aditya Bardia. Phase II study of talazoparib, a PARP inhibitor, in somatic BRCA1/2 mutant metastatic breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr OT-30-02.

Abstract PS17-02: Molecular alterations in the androgen receptor and associated clinical outcomes in hormone receptor-positive/HER2- metastatic breast cancer

Background: Although the androgen receptor (AR) is frequently co-expressed with ER and PR in hormone receptor-positive (HR+)/HER2- breast cancer, the biological significance of detectable AR alterations (ARalt) in metastatic disease (MBC) remains poorly understood. The primary objective of this study was to evaluate the association of ARalt status with clinical outcomes among women with HR+/HER2- MBC.

Methods: Retrospective review was performed on patients with HR+/HER2- MBC treated at an academic institution, for whom genotyping information was available. ARalt status was determined using Guardant360, a 73-gene next-generation sequencing assay that detects both AR mutations and amplifications in circulating tumor DNA. Women with positive or unknown HER2 status and triple-negative breast cancer were excluded from analysis, as were cases of male breast cancer. Time-to-progression on the therapy initiated immediately following Guardant testing was compared based on ARalt status, excluding patients treated with androgen-directed therapies given potential for confounding. Cumulative incidence plots were generated and analyzed by Gray’s test, and propensity score-adjusted competing risk models were generated with the probability of treatment as a function of age at metastatic diagnosis, presence of visceral metastasis, presence of de novo metastases, as well as number of prior therapies. Additional analysis was performed to assess progression stratified by treatment type (endocrine or non-endocrine based).

Results: Among women with HR+/HER2- MBC (n=222), 16 patients (7%) had detectable ARalt (12 point mutations, 4 amplifications). No baseline differences were observed between women with ARalt and those without AR alterations (ARwt), with respect to age at primary or metastatic diagnosis, menopause status, time to onset of metastasis or de novo metastatic disease, presence of visceral metastases, or number of endocrine/chemotherapies received prior to Guardant testing. ARalt tumors had a higher frequency of detected mutations (14% vs. 5%, p&lt;0.01), and frequently co-altered genes included TP53, PIK3CA, ERBB2, SMAD4, and NF1. Genes with a tendency towards co-alteration in ARalt but not in ARwt included MAP2K2, ARAF1, MAPK1, SMAD4, MYC, ROS1, TERT, and NRAS. In a multivariable model adjusting for age, de novo metastases, visceral metastases, and number of prior therapies, ARalt status was associated with a higher rate of progression (HR 2.5; 95% CI 1.2-5.0, p=0.01), particularly among patients treated with endocrine-based therapies following Guardant testing (HR 4.2, 95% CI 2.4-7.2, p&lt;0.0005) but was not statistically different in women treated with non-endocrine based therapies (HR 1.6; 95% CI 0.5-4.9, p=0.4).

Conclusions: ARalt tumors demonstrate a higher rate of progression on endocrine-based therapy as compared to ARwt tumors, highlighting a potential role of AR in mediating resistance to endocrine therapy in HR+/HER2- disease. Further translational investigations are warranted to determine whether ARalt/HR+/HER2- disease represents a unique biological subtype that predominantly relies on AR signaling and may thus benefit from blockade with AR antagonists.

Table 1. Multivariable competing risks model for endocrine progression.CovariatePFSMultivariableHR95% CIP-valuePositive ARalt status4.172.43-7.17&lt;0.01Age at metastatic dx1.000.97-1.020.89De novo metastasesYes1.770.96-3.260.07No[ref]Visceral metastasesYes1.250.72-2.160.43No[ref]No. of prior therapies1.060.93-1.210.98

Citation Format: Charles Dai, Andrzej Niemierko, Neelima Vidula, Laura M Spring, Seth A Wander, Arielle J Medford, Katherine A Hesler, Giuliana Malvarosa, Jeffrey Peppercorn, Dejan Juric, Steven J Isakoff, Beverly Moy, Leif W Ellisen, Aditya Bardia. Molecular alterations in the androgen receptor and associated clinical outcomes in hormone receptor-positive/HER2- metastatic breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS17-02.

Abstract PS18-19: Comparison of metastatic genomic profile in patients ≤45 years and patients &gt;45 years with triple-negative breast cancer

Background: Metastatic triple negative breast cancer (mTNBC) is often associated with aggressive biology, particularly in younger women. We hypothesized that the tumor genomic profile might vary based on age. The primary objective of this study was to compare the genomic profile, utilizing plasma-based targeted sequencing of common cancer related genes, in patients ≤45 years and &gt;45 years with mTNBC. The age cut-off of ≤ 45 was selected based on prior literature in TNBC using a similar cut-off for younger age stratification (Dolle, 2009).

Methods: A retrospective review of patients with mTNBC who had cell-free DNA (cfDNA) analysis (next generation sequencing, Guardant360®, 73 gene panel) collected at an academic institution after mTNBC diagnosis as part of clinical care from 1/2016-10/2019 was conducted. Patient age, demographics, and genotyping results were collected. Clinical and genomic characteristics were compared for patients ≤45 and &gt;45 using the Wilcoxon rank-sum test (continuous variables) and Pearson’s chi-squared test (categorical variables). Results:Of 74 patients with mTNBC and cfDNA results available, 17 were ≤45 years (median age 39 at mTNBC diagnosis), and 57 were &gt; 45 years (median age 58). In comparing patients ≤45 years with those &gt; 45 years, similar rates of de novo disease (≤45: 24%, &gt;45: 9%, p=0.10), visceral disease (≤45: 65%, &gt;45: 67%, p=0.88), and median number of prior lines of chemotherapy (≤45: 2, &gt; 45: 1, p=0.49) were observed. The percentage of patients with more than 1 detectable mutation (≤45: 94%, &gt;45: 93%, p=0.87), and median number of detected mutations (≤45: 5, &gt;45: 4, p=0.67) was similar between groups. However, the median mutant allele fraction (MAF; maximum) was significantly higher in patients ≤45 (≤45: median 29.8%; &gt;45: median 4.6%, p=0.006), and this finding remained significant after correcting for number of prior therapies. Table 1 depicts the mutation spectrum. While TP53 mutations were commonly seen in both cohorts, the median TP53 MAF was significantly higher in patients ≤45 years (≤45: 29.8%, &gt;45: 4.0%, p=0.015). PTEN mutations were found in a portion of patients &gt;45, but not identified in those ≤45 years. Amplifications in MYC, BRAF, PI3KCA, AR, CDK6, EGFR, MET, KIT, and CCND2 were seen more often in those ≤45 years, although these findings did not reach statistical significance. Survival outcomes will be presented at the meeting.

Conclusions:Patients with mTNBC diagnosed at ≤45 years had a significantly higher cfDNA MAF than those &gt;45, likely reflecting higher detectable tumor genomic burden. Mutations often associated with aggressive biology such as MYC, MET, and EGFR were more commonly found in patients ≤45, but the small sample size and limited statistical power makes it difficult to draw strong conclusions about differences in individual genes in this study. Further research with a larger multi-center cohort is ongoing to validate these findings.

Table 1.MutationAge ≤45Age &gt;45p-valueTP5376%75%0.93AR18%7%0.19BRCA118%12%0.57APC12%9%0.71NF112%7%0.53ERBB212%11%0.89BRCA26%9%0.70PTEN0%11%0.16AmplificationMYC29%19%0.37CCNE129%21%0.47BRAF29%14%0.14PI3KCA29%12%0.093AR24%7%0.054CDK624%12%0.25EGFR24%12%0.25MET24%11%0.17KIT18%7%0.19FGFR118%21%0.76CCND218%5%0.10PDGFRA12%7%0.53RAF112%7%0.53KRAS12%11%0.89CCND16%7%0.87

Citation Format: Neelima Vidula, Andrzej Niemierko, Katherine Hesler, Steven Isakoff, Dejan Juric, Jennifer Shin, Laura Spring, Jeffrey Peppercorn, Jerry Younger, Irene Kuter, Beverly Moy, Leif W. Ellisen, Aditya Bardia. Comparison of metastatic genomic profile in patients ≤45 years and patients &gt;45 years with triple-negative breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS18-19.

Abstract OT-03-06: Phase 2 study of response-guided neoadjuvant sacituzumab govitecan (IMMU-132) in patients with localized triple-negative breast cancer (NeoSTAR)

Background: Optimizing treatments for triple negative breast cancer (TNBC) in the localized breast cancer setting is key to preventing metastatic recurrences and reducing mortality from this devastating disease. Sacituzumab Govitecan (SG), a novel antibody-drug conjugate in which the topoisomerase 1 inhibitor SN-38 (the active metabolite of irinotecan) is coupled to a humanized monoclonal antibody targeting the tumor antigen Trop-2, was granted FDA accelerated approval in April 2020 for treatment of patients with metastatic TNBC. The NeoSTAR clinical trial is evaluating SG in the neoadjuvant setting for patients with localized TNBC. Trial design: This is a single arm phase II study of neoadjuvant SG in patients with localized TNBC. SG will be administered via an IV infusion on Days 1, 8 of each 21-day cycle at a starting dose of 10 mg/kg for 4 cycles. After 4 cycles, patients who have biopsy-proven residual disease will have the option to receive additional standard neoadjuvant therapy at the discretion of the treating physician and subsequently proceed to surgery. Those with a complete response on imaging may proceed directly to surgery. A baseline research biopsy prior to initiation of study therapy is required as well as tissue collection following treatment with SG (either at surgery or via biopsy prior to additional neoadjuvant therapy). Eligibility criteria: Patients ≥ 18 years of age with previously untreated primary TNBC as determined by the local institution according to ASCO/CAP criteria will be enrolled. Patients must either have a primary tumor &gt;1 cm measured by imaging (cT1c-T4), or be node positive. An ECOG performance score of 0 or 1, and adequate bone marrow, hepatic, and renal function is required. Specific aims: The primary objective is to assess the pathological complete response (pCR) rate in breast and lymph nodes (ypT0/isN0) with SG. Secondary objectives include assessment of radiological response rate, evaluation of the safety and tolerability of SG (CTCAE v5.0), disease-free survival (DFS), and quality of life (EORTC QLQ-C30). Exploratory objectives include assessment of potential predictive biomarkers, including Trop-2 expression, DNA damage response markers and immunological markers, as well as changes in cell free DNA with SG. Statistical methods: The primary analysis is based on the estimated pCR rate with SG and will be provided as a proportion (with two-sided 95% confidence interval). Accounting for up to a 14% drop out rate, a sample size of 43 patients will provide 80% power to exclude a lower limit of pCR of 20% (alpha 0.05, two-sided test). DFS will be analyzed using Kaplan-Meier methods and descriptive statistics. Target Accrual: 50 patients. Contact: Dr. Laura Spring (LSpring@mgh.harvard.edu) Clinicaltrials.gov #: NCT04230109

Citation Format: Laura M. Spring, Sara M. Tolaney, Neelam Desai, Amy Comander, Therese Mulvey, Ian E. Krop, Eric P. Winer, Elizabeth A. Mittendorf, Leif W. Ellisen, Aditya Bardia. Phase 2 study of response-guided neoadjuvant sacituzumab govitecan (IMMU-132) in patients with localized triple-negative breast cancer (NeoSTAR) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr OT-03-06.

A unique subset of glycolytic tumour-propagating cells drives squamous cell carcinoma

Head and neck squamous cell carcinoma (SCC) remains among the most aggressive human cancers. Tumour progression and aggressiveness in SCC are largely driven by tumour-propagating cells (TPCs). Aerobic glycolysis, also known as the Warburg effect, is a characteristic of many cancers; however, whether this adaptation is functionally important in SCC, and at which stage, remains poorly understood. Here, we show that the NAD+-dependent histone deacetylase sirtuin 6 is a robust tumour suppressor in SCC, acting as a modulator of glycolysis in these tumours. Remarkably, rather than a late adaptation, we find enhanced glycolysis specifically in TPCs. More importantly, using single-cell RNA sequencing of TPCs, we identify a subset of TPCs with higher glycolysis and enhanced pentose phosphate pathway and glutathione metabolism, characteristics that are strongly associated with a better antioxidant response. Together, our studies uncover enhanced glycolysis as a main driver in SCC, and, more importantly, identify a subset of TPCs as the cell of origin for the Warburg effect, defining metabolism as a key feature of intra-tumour heterogeneity.

An AMPK-dependent, non-canonical p53 pathway plays a key role in adipocyte metabolic reprogramming

It has been known adipocytes increase p53 expression and activity in obesity, however, only canonical p53 functions (i.e. senescence and apoptosis) are attributed to inflammation-associated metabolic phenotypes. Whether or not p53 is directly involved in mature adipocyte metabolic regulation remains unclear. Here we show p53 protein expression can be up-regulated in adipocytes by nutrient starvation without activating cell senescence, apoptosis, or a death-related p53 canonical pathway. Inducing the loss of p53 in mature adipocytes significantly reprograms energy metabolism and this effect is primarily mediated through a AMP-activated protein kinase (AMPK) pathway and a novel downstream transcriptional target, lysosomal acid lipase (LAL). The pathophysiological relevance is further demonstrated in a conditional and adipocyte-specific p53 knockout mouse model. Overall, these data support a non-canonical p53 function in the regulation of adipocyte energy homeostasis and indicate that the dysregulation of this pathway may be involved in developing metabolic dysfunction in obesity.

The adjuvant use of capecitabine for residual disease following pre-operative chemotherapy for breast cancer: Challenges applying CREATE-X to a US population

INTRODUCTION

The CREATE-X study, conducted in Japan and South Korea, established capecitabine as an adjuvant treatment option for patients with triple negative breast cancer (TNBC) who have residual disease (RD) following neoadjuvant anthracycline or taxane-based chemotherapy. However, there are no reports on the tolerability and outcomes of adjuvant capecitabine in the US setting following publication of the CREATE-X data.

METHODS

We retrospectively collected treatment and tolerability data from the medical records of the first 23 TNBC patients who received adjuvant capecitabine for RD post neoadjuvant chemotherapy at our institution. Disease-free survival was assessed using the Kaplan-Meier method.

RESULTS

The median starting dosage of capecitabine was 1871 mg/m²/day, most commonly divided into two daily doses on days 1-14 of each 21 day cycle. 34.8% of patients completed the treatment as prescribed. Side effects associated with treatment were common with 69.6% of patients experiencing hand-foot syndrome, 39.1% of patients experiencing diarrhea, and 13.0% of patients requiring hospitalization for side effects. Of 23 patients treated with adjuvant capecitabine, 34.8% completed the planned dose, 30.4% completed with dose reduction, and 34.8% discontinued early. At a median follow-up time of 14 months, the median disease-free survival was 22 months, with 30.4% of patients experiencing recurrence.

CONCLUSION

Tolerability was poor overall compared to the CREATE-X cohort. Administering adjuvant capecitabine for TNBC patients with residual disease in the United States is challenging given differences in tolerability. More research is needed to understand how poor tolerability will affect the efficacy of this approach in the US population.

Rising Circulating Tumor DNA As a Molecular Biomarker of Early Disease Progression in Metastatic Breast Cancer

PURPOSE

Accurate monitoring of therapeutic response remains an important unmet need for patients with metastatic breast cancer (MBC). Analysis of tumor genomics obtained via circulating tumor DNA (ctDNA) can provide a comprehensive overview of tumor evolution. Here, we evaluated ctDNA change as an early prognostic biomarker of subsequent radiologic progression and survival in MBC.

PATIENTS AND METHODS

Paired blood samples from patients with MBC were analyzed for levels of ctDNA, carcinoembryonic antigen, and cancer antigen 15-3 at baseline and during treatment. A Clinical Laboratory Improvement Amendments–certified sequencing panel of 73 genes was used to quantify tumor-specific point mutations in ctDNA. Multivariable logistic regression analysis was conducted to evaluate the association between ctDNA rise from baseline to during-treatment (genomic progression) and subsequent radiologic progression and progression-free survival (PFS).

RESULTS

Somatic mutations were detected in 76 baseline samples (90.5%) and 71 during-treatment samples (84.5%). Patients with genomic progression were more than twice as likely to have subsequent radiologic progression (odds ratio, 2.04; 95% CI, 1.74 to 2.41; P < .0001), with a mean lead time of 5.8 weeks. Genomic assessment provided a high positive predictive value of 81.8% and a negative predictive value of 89.7%. The subset of patients with genomic progression also had shorter PFS (median, 4.2 v 8.3 months; hazard ratio, 2.97; 95% CI, 1.75 to 5.04; log-rank P < .0001) compared with those without genomic progression.

CONCLUSION

Genomic progression, as assessed by early rise in ctDNA, is an independent biomarker of disease progression before overt radiologic or clinical progression becomes evident in patients with MBC.

Novel Agents for Metastatic Triple-Negative Breast Cancer: Finding the Positive in the Negative

Metastatic triple-negative breast cancer (TNBC) is associated with a poor prognosis, and the development of better therapeutics represents a major unmet clinical need. Although the mainstay of treatment of metastatic TNBC is chemotherapy, advances in genomics and molecular profiling have helped better define subtypes of TNBC with distinct biologic drivers to guide the therapeutic development of targeted therapies, including AKT inhibitors for PI3K/AKT-altered TNBC, checkpoint inhibitors for PD-L1-positive TNBC, and PARP inhibitors for BRCA1/2 mutant TNBC. This progress may ultimately convert TNBC from a disease traditionally defined by the absence of therapeutically actionable receptors to one that is defined by the presence of discrete molecular targets with therapeutic implications. Furthermore, antibody drug conjugates have emerged as an important therapeutic strategy to target genomically complex tumors that lack actionable oncogenes but have overexpressed actionable surface receptors such as trop-2. In this article, we discuss promising novel agents for advanced TNBC, some of which have been incorporated into current clinical practice, and others that will likely change the therapeutic landscape and redefine the TNBC terminology in the near future.

Cancer risks associated with the germline MITF(E318K) variant

The MITF(E318K) variant confers moderate risk for cutaneous melanoma. While there are small studies suggesting that this risk is associated with other malignancies (e.g. renal cell carcinoma), little is known about the role of this variant in specifying risk for other cancers. In this study, we perform a systematic review and meta-analysis of the published data as a backdrop to a whole-exome sequence(WES)-based characterization of MITF(E318K) risk for various cancers in sporadic samples from the TCGA and several genetically-enriched patient cohorts. We found minimal evidence of MITF(E318K)'s contribution to non-melanoma cancer risk among individuals with low inherited risks of melanoma (OR 1.168; 95% CI 0.78-1.74; p = 0.454), suggesting that earlier reports of an association between this variant and other malignancies may be related to shared environmental or polygenic risk factors rather than MITF(E318K). Interestingly, an association was observed with uterine carcinosarcoma, (OR 9.24; 95% CI 2.08-37.17; p = 0.024), which was not previously described. While more research needs to be completed, this study will help update cancer screening recommendations for patients with the MITF(E318K) variant.

Abstract 1903: PTEN loss mediates clinical cross-resistance to CDK4/6 and PI3Ká inhibitors in breast cancer

The combination of CDK4/6 inhibitors with anti-estrogen therapies significantly improves clinical outcomes in ER-positive advanced breast cancer. To identify mechanisms of acquired resistance, we analyzed serial biopsies and rapid autopsies from patients treated with the combination of the CDK4/6 inhibitor ribociclib with letrozole. This study revealed that some resistant tumors acquired RB loss, whereas other tumors lost PTEN expression at the time of progression. In breast cancer cells ablation of PTEN, through increased AKT activation, was sufficient to promote resistance to CDK4/6 inhibition in vitro and in vivo. Mechanistically, PTEN loss resulted in exclusion of p27 from the nucleus, leading to increased activation of both CDK4 and CDK2. Since PTEN loss also causes resistance to PI3Kα-inhibitors, currently approved in the post-CDK4/6 setting, these findings provide critical insight into how this single genetic event may cause clinical cross-resistance to multiple targeted therapies in the same patient, with implications for optimal treatment sequencing strategies.

Citation Format: Carlotta Costa, Ye Wang, Amy Ly, Yasuyuki Hosono, Ellen Murchie, Charlotte S. Walmsley, Tiffany Huynh, Christopher Healy, Rachel Peterson, Shogo Yanase, Charles T. Jakubik, Laura E. Henderson, Leah J. Damon, Daria Timonina, Ioannis Sanidas, Christopher J. Pinto, Mari Mino-Kenudson, James Stone, Nicholas J. Dyson, Leif W. Ellisen, Aditya Bardia, Hiromichi Ebi, Cyril H. Benes, Jeffrey A. Engelman, Dejan Juric. PTEN loss mediates clinical cross-resistance to CDK4/6 and PI3Ká inhibitors in breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1903.

Identification of Somatically Acquired BRCA1/2 Mutations by cfDNA Analysis in Patients with Metastatic Breast Cancer

PURPOSE

Plasma genotyping may identify mutations in potentially "actionable" cancer genes, such as BRCA1/2, but their clinical significance is not well-defined. We evaluated the characteristics of somatically acquired BRCA1/2 mutations in patients with metastatic breast cancer (MBC).

EXPERIMENTAL DESIGN

Patients with MBC undergoing routine cell-free DNA (cfDNA) next-generation sequencing (73-gene panel) before starting a new therapy were included. Somatic BRCA1/2 mutations were classified as known germline pathogenic mutations or novel variants, and linked to clinicopathologic characteristics. The effect of the PARP inhibitor, olaparib, was assessed in vitro, using cultured circulating tumor cells (CTCs) from a patient with a somatically acquired BRCA1 mutation and a second patient with an acquired BRCA2 mutation.

RESULTS

Among 215 patients with MBC, 29 (13.5%) had somatic cfDNA BRCA1/2 mutations [nine (4%) known germline pathogenic and rest (9%) novel variants]. Known germline pathogenic BRCA1/2 mutations were common in younger patients (P = 0.008), those with triple-negative disease (P = 0.022), and they were more likely to be protein-truncating alterations and be associated with TP53 mutations. Functional analysis of a CTC culture harboring a somatic BRCA1 mutation demonstrated high sensitivity to PARP inhibition, while another CTC culture harboring a somatic BRCA2 mutation showed no differential sensitivity. Across the entire cohort, APOBEC mutational signatures (COSMIC Signatures 2 and 13) and the "BRCA" mutational signature (COSMIC Signature 3) were present in BRCA1/2-mutant and wild-type cases, demonstrating the high mutational burden associated with advanced MBC.

CONCLUSIONS

Somatic BRCA1/2 mutations are readily detectable in MBC by cfDNA analysis, and may be present as both known germline pathogenic and novel variants.

Comparison of the cell-free DNA genomics in patients with metastatic breast cancer (MBC) who develop brain metastases versus those without brain metastases

1094

Background: The genomics of patients with metastatic breast cancer (MBC) who develop brain metastases (BM) is not well understood given the difficulty in obtaining brain tumor for genotyping. We compared tumor genotyping results via cell-free DNA (cfDNA) collected at MBC diagnosis in patients who developed BM after MBC diagnosis with those who did not develop BM (non-BM). Methods: Patients at an academic institution who had cfDNA testing (Guardant 360/Next generation sequencing, 73 gene assay) at MBC diagnosis between 1/2016-12/2017, with ≥ 6 months of follow-up post testing, were identified. A chart review was done to identify tumor subtype, demographics, cfDNA results, and development of BM at or after MBC diagnosis. Pearson’s chi-squared and Wilcoxon rank sum tests were used to determine differences in clinical and cfDNA characteristics in BM vs. non-BM (p<0.05 for statistical significance). Results: CfDNA results were available for 49 patients, of whom 13 (27%) developed BM (4 with BM at MBC diagnosis). The median time to BM development was 11 months. While patients with BM were younger at MBC diagnosis than non-BM (median age BM 53 vs. non-BM 61, p=0.05), they had similar subtype (BM vs. non-BM: HR+/HER2- 62% vs. 69%, HER2+ 8% vs. 14%, TNBC 23% vs. 17%, unknown 8% vs. 0%, p=0.3), de-novo vs. recurrent disease (BM vs. non-BM: de-novo 8% vs. 14%, recurrent 92% vs. 86%, p=0.6), and visceral disease (BM vs. non-BM: 77% vs. 56%, p=0.2) distributions. All patients with BM had ≥1 detectable cfDNA mutation vs. 88% of non-BM. While the median mutant allele frequency of the most common mutation was similar in BM vs. non-BM (2.4% vs. 3.7%, p=0.5), the mutation pattern varied. Patients with BM more often had mutations in BRCA1 (15% vs. 3%, p=0.1), APC (15% vs. 0%, p=0.02), and CDKN2A (15% vs. 0%, p=0.02), compared to non-BM. In 4 patients with BM at MBC diagnosis, mutations in APC (50%), CDKN2A (50%), and BRCA 1/2 (25%) were noted; 1 had coexisting APC and BRCA1/2 mutations and another had coexisting APC and CDKN2A mutations. Conclusions: Patients with MBC who develop BM may have different cfDNA genomics, particularly BRCA1, APC, and CDKN2A mutations. Further research is needed to determine the predictive value of cfDNA at MBC diagnosis in the identification of patients at higher risk of developing BM. [Table: see text]

Phase II trial of a PARP inhibitor in somatic BRCA mutant metastatic breast cancer

TPS1113

Background: Poly(ADP-ribose) polymerase (PARP) inhibitors are now approved for patients with germline BRCA1/2 mutated HER2 negative metastatic breast cancer (MBC). However, germline BRCA1/2 mutations only account for 5-10% of breast cancer. We previously demonstrated that a subset of MBC may harbor somatic BRCA1/2 mutations detectable by cell-free DNA (cfDNA) (Vidula, SABCS, 2017). We hypothesize that somatic BRCA1/2 mutant MBC may also respond to PARP inhibition, similar to ovarian cancer, where PARP inhibition is efficacious in both somatic and germline tumors (Oza, 2017). Methods: This single arm, open label, phase II clinical trial is evaluating the efficacy of talazoparib, a PARP inhibitor, in 30 patients with somatic pathogenic BRCA1/2 mutant MBC identified by cfDNA. Patients may have triple-negative disease with receipt of at least 1 prior chemotherapy regimen, or hormone receptor positive, HER2 negative disease with at least 1 prior hormone therapy for MBC. Patients may have received a prior platinum, in the absence of progression on platinum chemotherapy. Patients must not have a known germline BRCA1/2 mutation. Patients will be treated with talazoparib 1 mg daily until progression, unacceptable toxicity, or withdrawal of consent, with clinical exams monthly, scans (CT chest, abdomen, and pelvis, and bone scan as appropriate) every 3 months, and serial cfDNA collected monthly. The primary endpoint is progression-free survival, as defined by RECIST 1.1. Subjects are enrolled in a 2-stage design, which provides 80% power to demonstrate that treatment is associated with “success” (PFS > 12 weeks) in ³ 53% patients (4% alpha). Additional endpoints include objective response rate and toxicity (per NCI CTCAE version 5.0). Correlative endpoints include determining changes in BRCA1/2 mutant allele fraction, genomic evolution including emergence of BRCA reversion mutations, and the impact of biomarker changes on outcomes. This trial is currently enrolling patients at the Massachusetts General Hospital. Successful completion of this study may help expand the patient population that is able to benefit from PARP inhibition. Clinical trial information: NCT03990896 .

Phase Ib trial to evaluate safety and anti-tumor activity of the AKT inhibitor, ipatasertib, in combination with endocrine therapy and a CDK4/6 inhibitor for patients with hormone receptor positive (HR+)/HER2 negative metastatic breast cancer (MBC) (TAKTIC)

1066

Background: The cyclin-dependent kinase 4/6 inhibitors (CDK4/6i), with an anti-estrogen, are the standard of care for HR+/HER2- MBC. Insights from patient biopsies and preclinical analysis suggest that AKT1 activation can provoke CDK4/6i resistance. We hypothesized that targeting AKT1 following CDK4/6i progression may provide clinical benefit. Methods: TAKTIC is an open-label phase Ib trial exploring the combination of the AKT1 inhibitor, ipatasertib (ipat), with an aromatase inhibitor (Arm A), fulvestrant (Arm B), or the triplet combination (Arm C) of fulvestrant + ipat + palbociclib (palbo). The primary objective is to evaluate the safety and tolerability of ipat in combination with endocrine therapy +/- CDK4/6i. Key inclusion criteria include unresectable HR+/HER2- MBC; at least 1 prior therapy for MBC including any CDK4/6i; up to 2 prior lines of chemotherapy for MBC (no limit on prior endocrine therapy). Here, we present an interim analysis from the triplet combination (Arm C). Results: As of 1/31/2020, 25 pts have enrolled, including 12 on Arm C, all of whom received prior CDK4/6i (median no of prior lines = 5.5, range 2-7). Along with fulvestrant, 3 pts received ipat at 200mg + 125mg palbo, 7 pts received 300mg + 125mg palbo, and 2 pts received 400mg + 100mg palbo. To date, 8/12 pts remain on treatment including 2 with partial response, 3 with stable disease, 3 with restaging studies pending and 4 with progressive disease. The triplet combination was well tolerated. Grade 3 toxicities included reduced WBC (8/12), reduced neutrophil count (11/12), reduced lymphocyte count (2/12) and single instances of transaminitis, rash, and reduced platelet count. The only grade 4 toxicity was reduced neutrophil count (4/12). There were no DLTs observed and no discontinuations due to toxicity. Mean steady state pharmacokinetic parameters for ipat were similar to historical data from single agent trials suggesting that combined treatment with palbo + fulvestrant did not affect the pharmacokinetics of ipat. Updated analysis will be presented at the meeting. Conclusions: The triplet combination of endocrine therapy with CDK 4/6i and AKTi appears to be well tolerated in heavily pre-treated pts, with a subset demonstrating signs of clinical benefit. The trial demonstrates how insights into the molecular mechanisms of CDK4/6i resistance could be leveraged into actionable therapeutic regimens for HR+/HER2- MBC. Clinical trial information: NCT03959891 .

REDD1 loss reprograms lipid metabolism to drive progression of RAS mutant tumors

In this study, Qiao et al. set out to investigate the role of REDD1 in the development of KRAS-driven tumors. Using genetically engineered mouse models, the authors show that loss of REDD1 promotes the development of oncogenic KRAS-driven pancreatic and lung cancers. Additionally, the authors use a combination of transcriptomic and metabolomic analyses to show that REDD1 deficiency induces lipid uptake, enhances fatty acid oxidation, and suppresses de novo lipid biosynthesis, in particular under hypoxia conditions, which plays an important role for the redox homeostasis of tumor cells through the regulation of NADPH levels.

Human cancers with activating RAS mutations are typically highly aggressive and treatment-refractory, yet RAS mutation itself is insufficient for tumorigenesis, due in part to profound metabolic stress induced by RAS activation. Here we show that loss of REDD1, a stress-induced metabolic regulator, is sufficient to reprogram lipid metabolism and drive progression of RAS mutant cancers. Redd1 deletion in genetically engineered mouse models (GEMMs) of KRAS-dependent pancreatic and lung adenocarcinomas converts preneoplastic lesions into invasive and metastatic carcinomas. Metabolic profiling reveals that REDD1-deficient/RAS mutant cells exhibit enhanced uptake of lysophospholipids and lipid storage, coupled to augmented fatty acid oxidation that sustains both ATP levels and ROS-detoxifying NADPH. Mechanistically, REDD1 loss triggers HIF-dependent activation of a lipid storage pathway involving PPARγ and the prometastatic factor CD36. Correspondingly, decreased REDD1 expression and a signature of REDD1 loss predict poor outcomes selectively in RAS mutant but not RAS wild-type human lung and pancreas carcinomas. Collectively, our findings reveal the REDD1-mediated stress response as a novel tumor suppressor whose loss defines a RAS mutant tumor subset characterized by reprogramming of lipid metabolism, invasive and metastatic progression, and poor prognosis. This work thus provides new mechanistic and clinically relevant insights into the phenotypic heterogeneity and metabolic rewiring that underlies these common cancers.

Antibody-mediated delivery of viral epitopes to tumors harnesses CMV-specific T cells for cancer therapy

Several cancer immunotherapy approaches, such as immune checkpoint blockade and adoptive T-cell therapy, boost T-cell activity against the tumor, but these strategies are not effective in the absence of T cells specific for displayed tumor antigens. Here we outline an immunotherapy in which endogenous T cells specific for a noncancer antigen are retargeted to attack tumors. The approach relies on the use of antibody-peptide epitope conjugates (APECs) to deliver suitable antigens to the tumor surface for presention by HLA-I. To retarget cytomegalovirus (CMV)-specific CD8+ T cells against tumors, we used APECs containing CMV-derived epitopes conjugated to tumor-targeting antibodies via metalloprotease-sensitive linkers. These APECs redirect pre-existing CMV immunity against tumor cells in vitro and in mouse cancer models. In vitro, APECs activated specifically CMV-reactive effector T cells whereas a bispecific T-cell engager activated both effector and regulatory T cells. Our approach may provide an effective alternative in cancers that are not amenable to checkpoint inhibitors or other immunotherapies.

Abstract P2-21-01: Feasibility of a multidisciplinary diagnostic breast research biopsy project

Background: The comprehensive analysis of clinically annotated tissue specimens from those with either benign, high risk or malignant breast findings is critical to improve the understanding of breast cancer biology and treatment. Through a multidisciplinary team approach, we designed a protocol to allow a breast research biopsy to be collected with informed patient consent concurrent with the diagnostic biopsy at our institution. Here we describe the feasibility of the project.

Methods: IRB approval was obtained for the prospective collection and storage of clinically-annotated specimens, including breast biopsy cores, excess surgical tissue from breast surgery, and optional blood collection. Potential participants are identified through the list of scheduled breast biopsies at the Massachusetts General Hospital breast imaging center. Eligible patients are those ≥ age 18 undergoing a clinical breast biopsy. Research consent is obtained in the procedure room immediately following the clinical consent process and prior to the clinical biopsy. Following completion of standard clinical biopsy workflow, two research core biopsy specimens are obtained with a core biopsy needle ranging from 9 to 18 gauge. The first research specimen is flash frozen and stored on dry ice to preserve high molecular weight DNA and RNA. The second sample is cryopreserved in DMSO or a related agent to allow viable cell recovery. All consented patients are entered into a prospective database in REDCap. Medical records of the participating patients are reviewed periodically to collect data on patient demographics, tumor characteristics, and long-term outcomes.

Results: From 1/17/19 through 6/28/19, 144 patients were approached. 77.8% of patients consented, resulting in 96 lesions being biopsied for research. Of these, 45.8% were invasive carcinoma, 3.1% were DCIS, 6.1% were high risk lesions, and 44.8% were benign. Among the invasive breast cancers, 78.6% were hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-), 9.5% were HER2+, and 11.9% were triple negative.

Conclusion: We demonstrated that an upfront breast research biopsy program in patients presenting for initial diagnostic breast biopsy is feasible, with high rates of patient participation. Overall, 77.8% of approached subjects agreed to a concurrent research breast biopsy at the time of diagnostic biopsy. This approach may provide a high yield mechanism to generate a rich tissue repository with low cost and marginal additional time commitment by patient and providers that can support novel, cross-disciplinary research. A number of collaborative research projects are planned.

Citation Format: Kassidy Beyerlin, Christine Edmonds, Siang Boon Koh, Veerle Bossuyt, Annie Ma, Rachel Jimenez, Michelle Specht, Barbara L Smith, Brian Dontchos, Dennis Sgroi, Steven J Isakoff, Constance Lehman, Leif W Ellisen, Laura M Spring. Feasibility of a multidisciplinary diagnostic breast research biopsy project [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-21-01.

Abstract P3-11-03: Pilot neoadjuvant study of niraparib in HER2-negative, BRCA-mutated resectable breast cancer

Background: Niraparib is a selective poly(ADP-ribose) polymerase 1/2 inhibitor that has demonstrated antitumor activity in advanced triple-negative breast cancer (TNBC) in combination with a programmed cell death 1 inhibitor, with the greatest clinical activity seen in tumors with breast cancer susceptibility gene (BRCA) mutations. Pharmacologically, niraparib has demonstrated a wide volume of distribution and high cell membrane permeability. In breast and ovarian cancer xenograft mouse models, niraparib achieved tumor exposures that were 3.3 times greater than plasma exposure. The objective of this study is to evaluate the antitumor activity of single-agent niraparib in the neoadjuvant treatment of patients with localized, human epidermal growth factor receptor 2 (HER2)-negative, BRCA-mutated breast cancer. The relative concentration of niraparib in tumor versus plasma was also assessed. Methods: Eligible patients were ≥18 years old, with HER2-negative, BRCA-mutated (germline or somatic) resectable breast cancer with a tumor size of ≥1 cm who had not received prior treatment for the current malignancy. Patients received niraparib 200 mg once daily for 2 months. At the end of 2 months, at their treating physician’s discretion, patients proceeded directly to surgery, received additional cycles of niraparib (maximum of 6 months), or received neoadjuvant chemotherapy. The primary endpoint was tumor response rate measured by magnetic resonance imaging (MRI) after 2 months of treatment. Response was defined as a ≥30% reduction in tumor volume from baseline. Secondary endpoints included tumor response rate measured by ultrasound, quantified percent change in tumor volume measured by MRI or ultrasound, pathological complete response, and safety and tolerability. Additionally, niraparib concentrations were measured in tumor and plasma samples using qualified liquid chromatography-tandem mass spectrometry. Results: Twenty-one patients were enrolled. As of June 2019, 18 patients had both an MRI and ultrasound scan at the end of month 2 and were evaluable for response. Ten patients are currently on treatment. The median age of patients was 43 years (range, 21-73). Fourteen patients had a BRCA1 mutation, 6 patients had a BRCA2 mutation, and 1 patient had both. Fifteen patients had TNBC, and 6 patients had hormone receptor-positive disease. All 18 response-evaluable patients had a clinical response after 2 months of treatment by at least one imaging modality; no patient experienced disease progression. Tumor response rate measured by MRI after 2 months of treatment was 89% (n/N = 16/18). Results measured by ultrasound were similar, with a 94% response rate at cycle 2 (n/N = 17/18). The median percent decrease in tumor volume after 2 months of treatment was 88% (range, 26-100%) and 89% (range, 23-100%) as measured by MRI and ultrasound, respectively. In the 5 samples measured thus far, niraparib concentrations in tumor biopsies after 2 months of treatment ranged from approximately 4-131-fold higher than those in corresponding plasma samples. Efficacy and tumor concentration data for all patients will be presented at the meeting. The most common (≥10%) drug-related treatment-emergent adverse events (TEAEs) of any grade were nausea, fatigue, anemia, insomnia, and decreased appetite. The only drug-related grade ≥3 toxicity in ≥10% of patients was anemia (3 patients). Three patients had a dose reduction due to a TEAE; no patient discontinued treatment due to a TEAE. Conclusion: Niraparib was well tolerated and showed promising antitumor activity in the neoadjuvant treatment of patients with localized HER2-negative, BRCA-mutated breast cancer. Niraparib achieved 4-131-fold higher concentrations in tumor than in plasma. Clinical trial information: NCT03329937. Funding: TESARO: A GSK Company (Waltham, MA, USA) sponsored the study.

Citation Format: Hyo Han, Minetta C Liu, Erika Hamilton, Hanna Irie, Cesar A Santa-Maria, James Reeves, Andre Liem, Adrianna Milillo Naraine, Julie Nangia, David Page, Meghan Duncan, Ming Shan, Yongqiang Tang, Julie R Graham, Leif W Ellisen, Steven Isakoff, Laura Spring. Pilot neoadjuvant study of niraparib in HER2-negative, BRCA-mutated resectable breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-11-03.