A randomized phase III double-blind placebo-controlled trial of first line chemotherapy and trastuzumab with or without bevacizumab for patients with HER2/neu-positive metastatic breast cancer: a trial of the ECOG-ACRIN Cancer Research Group (E1105)

Background

In 2008, bevacizumab received accelerated Food and Drug Administration (FDA) approval for use in human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (MBC). Based on the preclinical and preliminary clinical activity of the trastuzumab and bevacizumab combination, ECOG-ACRIN E1105 trial was developed to determine if the addition of bevacizumab to a chemotherapy and trastuzumab combination for first-line therapy would improve progression-free survival (PFS) in patients with HER2-positive MBC.

Findings

96 patients were randomized to receive standard first-line chemotherapy and trastuzumab with or without bevacizumab between November 2007 and October 2009, and 93 began protocol therapy. Induction therapy was given for 24 weeks, followed by maintenance trastuzumab with or without bevacizumab. 60% (56/93) began carboplatin and 74% (69/93) completed 6 cycles of induction therapy. Primary endpoint was PFS. Median PFS was 11.1 and 13.8 months for placebo and bevacizumab arms, respectively (hazard ratio [HR] 95%, Confidence Interval [Cl] for bevacizumab vs. placebo: 0.73 [0.43-1.23], p = 0.24), and at a median follow-up of 70.7 months, median survival was 49.1 and 63 months (HR [95% Cl] for OS: 1.09 [0.61-1.97], p = 0.75). The most common toxicities across both arms were neutropenia and hypertension, with left ventricular systolic dysfunction, fatigue, and sensory neuropathy reported more frequently with bevacizumab.

Conclusions

In this trial, the addition of bevacizumab did not improve outcomes in patients with metastatic HER2-positive breast cancer. Although the trial was underpowered due to smaller than anticipated sample size, these findings corroborated other clinical trials during this time.

Pharmacological suppression of the OTUD4/CD73 proteolytic axis revives antitumor immunity against immune-suppressive breast cancers

Despite widespread utilization of immunotherapy, treating immune-cold tumors remains a challenge. Multiomic analyses and experimental validation identified the OTUD4/CD73 proteolytic axis as a promising target in treating immune-suppressive triple negative breast cancer (TNBC). Mechanistically, deubiquitylation of CD73 by OTUD4 counteracted its ubiquitylation by TRIM21, resulting in CD73 stabilization inhibiting tumor immune responses. We further demonstrated the importance of TGF-β signaling for orchestrating the OTUD4/CD73 proteolytic axis within tumor cells. Spatial transcriptomics profiling discovered spatially resolved features of interacting malignant and immune cells pertaining to expression levels of OTUD4 and CD73. In addition, ST80, a newly developed inhibitor, specifically disrupted proteolytic interaction between CD73 and OTUD4, leading to reinvigoration of cytotoxic CD8+ T cell activities. In preclinical models of TNBC, ST80 treatment sensitized refractory tumors to anti-PD-L1 therapy. Collectively, our findings uncover what we believe to be a novel strategy for targeting the immunosuppressive OTUD4/CD73 proteolytic axis in treating immune-suppressive breast cancers with the inhibitor ST80.

Lasofoxifene versus fulvestrant for ER+/HER2- metastatic breast cancer with an ESR1 mutation: results from the randomized, phase II ELAINE 1 trial

BACKGROUND

Acquired estrogen receptor alpha (ER/ESR1) mutations commonly cause endocrine resistance in ER+ metastatic breast cancer (mBC). Lasofoxifene, a novel selective ER modulator, stabilizes an antagonist conformation of wild-type and ESR1-mutated ER-ligand binding domains, and has antitumor activity in ESR1-mutated xenografts.

PATIENTS AND METHODS

In this open-label, randomized, phase II, multicenter, ELAINE 1 study (NCT03781063), we randomized women with ESR1-mutated, ER+/human epidermal growth factor receptor 2 negative (HER2-) mBC that had progressed on an aromatase inhibitor (AI) plus a cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) to oral lasofoxifene 5 mg daily or IM fulvestrant 500 mg (days 1, 15, and 29, and then every 4 weeks) until disease progression/toxicity. The primary endpoint was progression-free survival (PFS); secondary endpoints were safety/tolerability.

RESULTS

A total of 103 patients received lasofoxifene (n = 52) or fulvestrant (n = 51). The most current efficacy analysis showed that lasofoxifene did not significantly prolong median PFS compared with fulvestrant: 24.2 weeks (∼5.6 months) versus 16.2 weeks (∼3.7 months; P = 0.138); hazard ratio 0.699 (95% confidence interval 0.434-1.125). However, PFS and other clinical endpoints numerically favored lasofoxifene: clinical benefit rate (36.5% versus 21.6%; P = 0.117), objective response rate [13.2% (including a complete response in one lasofoxifene-treated patient) versus 2.9%; P = 0.124], and 6-month (53.4% versus 37.9%) and 12-month (30.7% versus 14.1%) PFS rates. Most common treatment-emergent adverse events with lasofoxifene were nausea, fatigue, arthralgia, and hot flushes. One death occurred in the fulvestrant arm. Circulating tumor DNA ESR1 mutant allele fraction (MAF) decreased from baseline to week 8 in 82.9% of evaluable lasofoxifene-treated versus 61.5% of fulvestrant-treated patients.

CONCLUSIONS

Lasofoxifene demonstrated encouraging antitumor activity versus fulvestrant and was well tolerated in patients with ESR1-mutated, endocrine-resistant mBC following progression on AI plus CDK4/6i. Consistent with target engagement, lasofoxifene reduced ESR1 MAF, and to a greater extent than fulvestrant. Lasofoxifene may be a promising targeted treatment for patients with ESR1-mutated mBC and warrants further investigation.

Identifying homologous recombination deficiency in breast cancer: genomic instability score distributions differ among breast cancer subtypes

PURPOSE

A 3-biomarker homologous recombination deficiency (HRD) score is a key component of a currently FDA-approved companion diagnostic assay to identify HRD in patients with ovarian cancer using a threshold score of ≥ 42, though recent studies have explored the utility of a lower threshold (GIS ≥ 33). The present study evaluated whether the ovarian cancer thresholds may also be appropriate for major breast cancer subtypes by comparing the genomic instability score (GIS) distributions of BRCA1/2-deficient estrogen receptor-positive breast cancer (ER + BC) and triple-negative breast cancer (TNBC) to the GIS distribution of BRCA1/2-deficient ovarian cancer.

METHODS

Ovarian cancer and breast cancer (ER + BC and TNBC) tumors from ten study cohorts were sequenced to identify pathogenic BRCA1/2 mutations, and GIS was calculated using a previously described algorithm. Pathologic complete response (pCR) to platinum therapy was evaluated in a subset of TNBC samples. For TNBC, a threshold was set and threshold validity was assessed relative to clinical outcomes.

RESULTS

A total of 560 ovarian cancer, 805 ER + BC, and 443 TNBC tumors were included. Compared to ovarian cancer, the GIS distribution of BRCA1/2-deficient samples was shifted lower for ER + BC (p = 0.015), but not TNBC (p = 0.35). In the subset of TNBC samples, univariable logistic regression models revealed that GIS status using thresholds of ≥ 42 and ≥ 33 were significant predictors of response to platinum therapy.

CONCLUSIONS

This study demonstrated that the GIS thresholds used for ovarian cancer may also be appropriate for TNBC, but not ER + BC. GIS thresholds in TNBC were validated using clinical response data to platinum therapy.

Interplay between ESR1/PIK3CA codon variants, oncogenic pathway alterations and clinical phenotype in patients with metastatic breast cancer (MBC): comprehensive circulating tumor DNA (ctDNA) analysis

BACKGROUND

although being central for the biology and druggability of hormone-receptor positive, HER2 negative metastatic breast cancer (MBC), ESR1 and PIK3CA mutations are simplistically dichotomized as mutated or wild type in current clinical practice.

METHODS

The study analyzed a multi-institutional cohort comprising 703 patients with luminal-like MBC characterized for circulating tumor DNA through next generation sequencing (NGS). Pathway classification was defined based on previous work (i.e., RTK, RAS, RAF, MEK, NRF2, ER, WNT, MYC, P53, cell cycle, notch, PI3K). Single nucleotide variations (SNVs) were annotated for their oncogenicity through OncoKB. Only pathogenic variants were included in the models. Associations among clinical characteristics, pathway classification, and ESR1/PIK3CA codon variants were explored.

RESULTS

The results showed a differential pattern of associations for ESR1 and PIK3CA codon variants in terms of co-occurring pathway alterations patterns of metastatic dissemination, and prognosis. ESR1 537 was associated with SNVs in the ER and RAF pathways, CNVs in the MYC pathway and bone metastases, while ESR1 538 with SNVs in the cell cycle pathway and liver metastases. PIK3CA 1047 and 542 were associated with CNVs in the PI3K pathway and with bone metastases.

CONCLUSIONS

The study demonstrated how ESR1 and PIK3CA codon variants, together with alterations in specific oncogenic pathways, can differentially impact the biology and clinical phenotype of luminal-like MBC. As novel endocrine therapy agents such as selective estrogen receptor degraders (SERDS) and PI3K inhibitors are being developed, these results highlight the pivotal role of ctDNA NGS to describe tumor evolution and optimize clinical decision making.

Dynamic Glycoprotein Hyposialylation Promotes Chemotherapy Evasion and Metastatic Seeding of Quiescent Circulating Tumor Cell Clusters in Breast Cancer

Most circulating tumor cells (CTC) are detected as single cells, whereas a small proportion of CTCs in multicellular clusters with stemness properties possess 20- to 100-times higher metastatic propensity than the single cells. Here we report that CTC dynamics in both singles and clusters in response to therapies predict overall survival for breast cancer. Chemotherapy-evasive CTC clusters are relatively quiescent with a specific loss of ST6GAL1-catalyzed α2,6-sialylation in glycoproteins. Dynamic hyposialylation in CTCs or deficiency of ST6GAL1 promotes cluster formation for metastatic seeding and enables cellular quiescence to evade paclitaxel treatment in breast cancer. Glycoproteomic analysis reveals newly identified protein substrates of ST6GAL1, such as adhesion or stemness markers PODXL, ICAM1, ECE1, ALCAM1, CD97, and CD44, contributing to CTC clustering (aggregation) and metastatic seeding. As a proof of concept, neutralizing antibodies against one newly identified contributor, PODXL, inhibit CTC cluster formation and lung metastasis associated with paclitaxel treatment for triple-negative breast cancer.

SIGNIFICANCE

This study discovers that dynamic loss of terminal sialylation in glycoproteins of CTC clusters contributes to the fate of cellular dormancy, advantageous evasion to chemotherapy, and enhanced metastatic seeding. It identifies PODXL as a glycoprotein substrate of ST6GAL1 and a candidate target to counter chemoevasion-associated metastasis of quiescent tumor cells. This article is featured in Selected Articles from This Issue, p. 1949.

Randomized Phase II Trial of Endocrine Therapy With or Without Ribociclib After Progression on Cyclin-Dependent Kinase 4/6 Inhibition in Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Metastatic Breast Cancer: MAINTAIN Trial

PURPOSE

Cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) with endocrine therapy (ET) improves progression-free survival (PFS) and overall survival (OS) in hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (MBC). Although preclinical and clinical data demonstrate a benefit in changing ET and continuing a CDK4/6i at progression, no randomized prospective trials have evaluated this approach.

METHODS

In this investigator-initiated, phase II, double-blind placebo-controlled trial in patients with HR+/HER2- MBC whose cancer progressed during ET and CDK4/6i, participants switched ET (fulvestrant or exemestane) from ET used pre-random assignment and randomly assigned 1:1 to the CDK4/6i ribociclib versus placebo. PFS was the primary end point, defined as time from random assignment to disease progression or death. Assuming a median PFS of 3.8 months with placebo, we had 80% power to detect a hazard ratio (HR) of 0.58 (corresponding to a median PFS of at least 6.5 months with ribociclib) with 120 patients randomly assigned using a one-sided log-rank test and significance level set at 2.5%.

RESULTS

Of the 119 randomly assigned participants, 103 (86.5%) previously received palbociclib and 14 participants received ribociclib (11.7%). There was a statistically significant PFS improvement for patients randomly assigned to switched ET plus ribociclib (median, 5.29 months; 95% CI, 3.02 to 8.12 months) versus switched ET plus placebo (median, 2.76 months; 95% CI, 2.66 to 3.25 months) HR, 0.57 (95% CI, 0.39 to 0.85); P = .006. At 6 and 12 months, the PFS rate was 41.2% and 24.6% with ribociclib, respectively, compared with 23.9% and 7.4% with placebo.

CONCLUSION

In this randomized trial, there was a significant PFS benefit for patients with HR+/HER2- MBC who switched ET and received ribociclib compared with placebo after previous CDK4/6i and different ET.

NCCN Guidelines® Insights: Breast Cancer, Version 4.2023

The NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines) for Breast Cancer address all aspects of management for breast cancer. The treatment landscape of metastatic breast cancer is evolving constantly. The therapeutic strategy takes into consideration tumor biology, biomarkers, and other clinical factors. Due to the growing number of treatment options, if one option fails, there is usually another line of therapy available, providing meaningful improvements in survival. This NCCN Guidelines Insights report focuses on recent updates specific to systemic therapy recommendations for patients with stage IV (M1) disease.

Margetuximab in HER2-positive metastatic breast cancer

Several anti-HER2 agents are approved for third-line treatment and beyond (after first-line and second-line); however, no specific treatment strategy is recommended for third-line and beyond. Although these agents improve disease outcomes, HER2-positive metastatic breast cancer remains incurable and there is an unmet need for effective therapies in the later line setting. This review focuses on the development of margetuximab-cmkb, a novel, Fc-engineered, anti-HER2 monoclonal antibody, and its role in the systemic treatment of adult patients with metastatic HER2-positive breast cancer who have received two or more prior anti-HER2 regimens, at least one of which was for metastatic disease.

Cyclin-Dependent Kinase 4/6 Inhibitors Beyond Progression in Metastatic Breast Cancer: A Retrospective Real-World Biomarker Analysis

PURPOSE

As the continuation beyond progression (BP) of cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) is becoming increasingly attractive for the treatment of patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (MBC), the definition of resistance factors is crucial. The aim of the study was to investigate the impact of CDK 4/6i BP and to explore potential genomic stratification factors.

MATERIALS AND METHODS

We retrospectively analyzed a multi-institutional cohort of patients with HR-positive HER2-negative MBC characterized for circulating tumor DNA through next-generation sequencing before treatment start. Differences across subgroups were analyzed by chi-square test, and survival was tested by univariable and multivariable Cox regression. Further correction was applied by propensity score matching.

RESULTS

Among the 214 patients previously exposed to CDK4/6i, 172 were treated with non-CDK4/6i-based treatment (non-CDK) and 42 with CDK4/6i BP. Multivariable analysis showed a significant impact of CDK4/6i BP, TP53 single-nucleotide variants, liver involvement, and treatment line on both progression-free survival (PFS) and overall survival (OS). Propensity score matching confirmed the prognostic role of CDK4/6i BP both for PFS and OS. The favorable impact of CDK4/6i BP was consistent across all subgroups, and a differential benefit was suggested for ESR1-mutated patients. ESR1 and RB1 mutations were more represented in the CDK4/6i BP subgroup with respect to CDK4/6i upfront.

CONCLUSION

The study highlighted a significant prognostic impact of the CDK4/6i BP strategy with a potential added benefit in patients with ESR1 mutations suggesting the need for an extensive biomarker characterization.

Computational ranking-assisted identification of Plexin-B2 in homotypic and heterotypic clustering of circulating tumor cells in breast cancer metastasis

Metastasis is the cause of over 90% of all deaths associated with breast cancer, yet the strategies to predict cancer spreading based on primary tumor profiles and therefore prevent metastasis are egregiously limited. As rare precursor cells to metastasis, circulating tumor cells (CTCs) in multicellular clusters in the blood are 20-50 times more likely to produce viable metastasis than single CTCs. However, the molecular mechanisms underlying various CTC clusters, such as homotypic tumor cell clusters and heterotypic tumor-immune cell clusters, are yet to be fully elucidated. Combining machine learning-assisted computational ranking with experimental demonstration to assess cell adhesion candidates, we identified a transmembrane protein Plexin- B2 (PB2) as a new therapeutic target that drives the formation of both homotypic and heterotypic CTC clusters. High PB2 expression in human primary tumors predicts an unfavorable distant metastasis-free survival and is enriched in CTC clusters compared to single CTCs in advanced breast cancers. Loss of PB2 reduces formation of homotypic tumor cell clusters as well as heterotypic tumor-myeloid cell clusters in triple-negative breast cancer. Interactions between PB2 and its ligand Sema4C on tumor cells promote homotypic cluster formation, and PB2 binding with Sema4A on myeloid cells (monocytes) drives heterotypic CTC cluster formation, suggesting that metastasizing tumor cells hijack the PB2/Sema family axis to promote lung metastasis in breast cancer. Additionally, using a global proteomic analysis, we identified novel downstream effectors of the PB2 pathway associated with cancer stemness, cell cycling, and tumor cell clustering in breast cancer. Thus, PB2 is a novel therapeutic target for preventing new metastasis.

A phase I/II study of intrathecal trastuzumab in human epidermal growth factor receptor 2-positive (HER2-positive) cancer with leptomeningeal metastases: Safety, efficacy, and cerebrospinal fluid pharmacokinetics

BACKGROUND

Patients with human epidermal growth factor receptor 2-positive (HER2-positive) cancers have a high incidence of central nervous system (CNS) spread, but unfortunately systemic trastuzumab which targets the HER2 receptor has little CNS penetration. The purpose of this study was to determine the maximum-tolerated dose of intrathecal trastuzumab and its efficacy in patients with HER2-positive leptomeningeal disease (LMD).

METHODS

This multicenter study enrolled 34 LMD patients in a combined phase I/II study in treating patients with intrathecal trastuzumab. Any HER2-positive histology was allowed in the phase I; the phase II was limited to HER2-positive breast cancer.

RESULTS

Intrathecal trastuzumab was well-tolerated, with one dose limiting toxicity of grade 4 (arachnoiditis) occurring at the 80 mg twice weekly dose. The recommended phase II dose was 80 mg intrathecally twice weekly. Twenty-six patients at dose level 80 mg were included in evaluation for efficacy: partial response was seen in 5 (19.2%) patients, stable disease was observed in 13 (50.0%), and 8 (30.8%) of the patients had progressive disease. Median overall survival (OS) for phase II dose treated patients was 8.3 months (95% CI 5.2-19.6). The phase II HER2-positive breast cancer patients median OS was 10.5 months (95% CI 5.2-20.9). Pharmacokinetic (PK) studies were limited in the setting of concurrent systemic trastuzumab administration, however, did show stable cerebrospinal fluid (CSF) concentrations with repeated dosing suggest that trastuzumab does not accumulate in the CSF in toxic concentrations.

CONCLUSION

This study suggests promise for potentially improved outcomes of HER-positive LMD patients when treated with intrathecal trastuzumab while remaining safe and well-tolerated for patients.

Margetuximab Versus Trastuzumab in Patients With Previously Treated HER2-Positive Advanced Breast Cancer (SOPHIA): Final Overall Survival Results From a Randomized Phase 3 Trial

Clinical trials frequently include multiple end points that mature at different times. The initial report, typically based on the primary end point, may be published when key planned co-primary or secondary analyses are not yet available. Clinical Trial Updates provide an opportunity to disseminate additional results from studies, published in JCO or elsewhere, for which the primary end point has already been reported.Final overall survival (OS) in SOPHIA (ClinicalTrials.gov identifier: NCT02492711), a study of margetuximab versus trastuzumab, both with chemotherapy, in patients with previously treated human epidermal growth factor receptor 2-positive advanced breast cancer, is reported with updated safety. Overall, 536 patients in the intention-to-treat population were randomly assigned to margetuximab (15 mg/kg intravenously once every 3 weeks; n = 266) plus chemotherapy or trastuzumab (6 mg/kg intravenously once every 3 weeks after a loading dose of 8 mg/kg; n = 270) plus chemotherapy. Primary end points were progression-free survival, previously reported, and OS. Final OS analysis was triggered by 385 prespecified events. The median OS was 21.6 months (95% CI, 18.89 to 25.07) with margetuximab versus 21.9 months (95% CI, 18.69 to 24.18) with trastuzumab (hazard ratio [HR], 0.95; 95% CI, 0.77 to 1.17; P = .620). Preplanned, exploratory analysis of CD16A genotyping suggested a possible improvement in OS for margetuximab in CD16A-158FF patients versus trastuzumab (median OS, 23.6 v 19.2 months; HR, 0.72; 95% CI, 0.52 to 1.00) and a possible improvement in OS for trastuzumab in CD16A-158VV patients versus margetuximab (median OS, 31.1 v 22.0 months; HR, 1.77; 95% CI, 1.01 to 3.12). Margetuximab safety was comparable with trastuzumab. Final overall OS analysis did not demonstrate margetuximab advantage over trastuzumab. Margetuximab studies in patients with human epidermal growth factor receptor 2-positive breast cancer with different CD16A allelic variants are warranted.

Proteolytic regulation of CD73 by TRIM21 orchestrates tumor immunogenicity

Despite the rapid utilization of immunotherapy, emerging challenges to the current immune checkpoint blockade need to be resolved. Here, we report that elevation of CD73 levels due to its aberrant turnover is correlated with poor prognosis in immune-cold triple-negative breast cancers (TNBCs). We have identified TRIM21 as an E3 ligase that governs CD73 destruction. Disruption of TRIM21 stabilizes CD73 that in turn enhances CD73-catalyzed production of adenosine, resulting in the suppression of CD8+ T cell function. Replacement of lysine 133, 208, 262, and 321 residues by arginine on CD73 attenuated CD73 ubiquitylation and degradation. Diminishing of CD73 ubiquitylation remarkably promotes tumor growth and impedes antitumor immunity. In addition, a TRIM21high/CD73low signature in a subgroup of human breast malignancies was associated with a favorable immune profile. Collectively, our findings uncover a mechanism that governs CD73 proteolysis and point to a new therapeutic strategy by modulating CD73 ubiquitylation.

Breast Cancer, Version 3.2022, NCCN Clinical Practice Guidelines in Oncology

The therapeutic options for patients with noninvasive or invasive breast cancer are complex and varied. These NCCN Clinical Practice Guidelines for Breast Cancer include recommendations for clinical management of patients with carcinoma in situ, invasive breast cancer, Paget disease, phyllodes tumor, inflammatory breast cancer, and management of breast cancer during pregnancy. The content featured in this issue focuses on the recommendations for overall management of ductal carcinoma in situ and the workup and locoregional management of early stage invasive breast cancer. For the full version of the NCCN Guidelines for Breast Cancer, visit NCCN.org.

NCCN Guidelines Updates: Management of Patients With HER2-Negative Breast Cancer

Treatment for metastatic HER2-negative breast cancer is becoming increasingly individualized as more of the tumor landscape is described and drugs are developed to target its pathways. Survival can be prolonged by CDK4/6 inhibitors in patients with hormone receptor–positive tumors and by immunotherapy in those with triple-negative disease. In patients with BRCA1/2 mutations, PARP inhibitors delay disease progression. Antibody–drug conjugates are expected to become critical components of the treatment landscape, and targeted drugs are proving to benefit small subsets of patients.

Abstract P1-02-11: Somatic alterations and PD-L1 positivity in advanced breast cancer

Background: With the recent FDA approvals of atezolizumab and pembrolizumab for the treatment of unresectable locally advanced or metastatic triple-negative breast cancer, immuno-oncology (IO) therapy has become feasible for the first time in breast cancer, and PD-L1 immunohistochemistry (IHC) has become an essential assay in breast cancer diagnostics. However, relatively little is known about the molecular profile of PD-L1+ breast cancers compared to other tumors, such as lung cancer. Furthermore, although the initial data have shown the most benefit in triple-negative patients, it is unclear whether additional subgroups of patients with advanced breast cancer enriched for PD-L1 expression can be identified, and, therefore, might benefit from IO therapy. Methods: We identified 60 women with locally advanced or metastatic breast cancer who underwent next generation sequencing (NGS) of tumor samples obtained at our institution as part of their clinical care and performed PD-L1 testing using the Ventana SP142 platform. Samples were considered positive for PD-L1 if ≥1%. The NGS assay was designed to detect single nucleotide variants, insertions and deletions, copy number variants, and specific translocations in approximately 600 genes. Associations between PD-L1 status, molecular alterations, and tumor histopathologic features were assessed, with P < 0.05 considered statistically significant. Results: Our cohort consisted of 60 women at a median age of 56 years (range 31-81). 50% of samples were from primary tumors within the breast, 15% were from regional lymph node metastases, and 35% were from distant metastatic sites. Most tumors showed ductal histology (80%) and were either grade 2 (38%) or grade 3 (57%), while half showed focal (27%) or extensive (23%) necrosis. Based on IHC, most tumors were Luminal B (54%), followed by triple-negative (25%), Luminal A (13%), and HER2-enriched (8%) tumors. About one third of tumors had either moderate (25%) or marked (8%) TILs, and about half showed positivity for PD-L1 (48%). Most tumors had a low tumor mutational burden (TMB), with 83% having <5, 14% having 5-9, and 3% having ≥10 mutations per Mb. The median number of genes with reportable somatic alterations was 2 (IQR 1-3). The most common genes with somatic alterations were TP53 (51%), PIK3CA (23%), ERBB2 (16%), ESR1 (14%), FGFR1 (9%), AKT1 (7%), CDH1 (7%), GATA3 (7%), MYC (7%), and CCND1 (5%). 50% of luminal A, 38% of luminal B, 50% of HER2-enriched, and 75% of triple-negative tumors were PD-L1+, although this difference was not statistically significant (P = 0.22). PD-L1 positivity was more likely in grade 3 tumors (62% vs 31% grade 1-2, P = 0.02), and in tumors with extensive necrosis (85% vs 37% absent/focal, P = 0.004). Of all the genes tested, only TP53 was significantly associated with being PD-L1+ (69% TP53-mutant vs 32% TP53-wild-type; P = 0.008). Neither number of somatic alterations (P = 0.60) or TMB (P = 0.08) were significantly associated with PD-L1+ tumors. Of note, 53% of non-triple-negative PD-L1+ tumors had mutations in TP53, and 60% of non-triple-negative tumors with TP53 mutations were PD-L1+. Conclusions: Our data suggest that PD-L1 positivity is relatively common in patients with locally advanced or metastatic breast cancer, not only in triple-negative breast cancer but in all breast cancer subtypes. In addition, TP53 mutation is significantly associated with an increased likelihood of positivity for PD-L1, including in non-triple-negative tumors. This correlation could potentially be a useful marker for selecting non-triple-negative breast cancer patients for PD-L1 testing and, if positive, potentially offer them IO options for optimizing their response to therapy.

Citation Format: Brian S Finkelman, Massimo Cristofanilli, Luis Z Blanco, Jr, Amir Behdad, Leonidas C Platanias, William J Gradishar, Kalliopi P Siziopikou. Somatic alterations and PD-L1 positivity in advanced breast cancer [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 P1-02-11.

Abstract PD14-01: Comprehensive molecular characterization of patients with metastatic invasive lobular carcinoma (ILC): Using real-world data to describe this unique clinical entity

Background: ILC is the second most common type of breast cancer and accounts for approximately 10% of all invasive breast cancers. A hallmark of ILC is the lack of E-cadherin (CDH1) expression, which is frequently used to discriminate between lesions with borderline ductal and lobular histologies. While the genomic landscape of primary ILCs has been well described, less is known about patients (pts) with metastatic-ILC (mILC). Better characterization of the genomic landscape associated with mILC is critical for identifying biomarkers that may provide new insight into ILC tumor biology and ultimately improve long-term outcomes in pts with mILC. Methods: We retrospectively analyzed de-identified next-generation sequencing (NGS) data from 150 advanced/metastatic pts with ILC and 51 with mixed lobular/ductal histology, defined using the histology of the sequenced biopsy. Diagnoses were abstracted from pathology reports submitted at the time of sequencing. We used the stage documented closest in time to biopsy collection, and samples were excluded if the staging date was unknown or exceeded 180 days after the biopsy date. Our dataset consisted of samples that were molecularly profiled using the Tempus xT solid tumor assay (DNA-seq of 595-648 genes at 500x coverage, full-transcriptome RNA-seq). The mutations identified for this study include somatic single-nucleotide variants and insertions/deletions. Furthermore, we examined the co-mutational landscape of CDH1-mutant disease and investigated transcript-level expression variation. Results: Mutations in CDH1 occurred in 65.3% of all mILC samples (98/150). CDH1 expression was similar between CDH1-mutant and WT mILC samples (Wilcoxon rank sum test, p=0.8). The median tumor mutational burden (TMB) score was significantly higher in CDH1-mutant samples (Wilcoxon rank-sum test, p=0.010). CDH1-mutant samples were more likely to have a high TMB (≥10 mutations/MB) when compared with the wild-type CDH1 cohort (10% vs. 6.2%), but this difference was not statistically significant (Fisher’s Exact test, p=0.5). Additionally, we observed that the ER+ subtype was more frequent in CDH1-mutant samples, although this difference was not statistically significant (97% vs 88%; Fisher’s exact test, p=0.063). PIK3CA mutations were enriched in CDH1-mutant mILC (Table 1). TBX3 and NCOR1 mutations were also mildly enriched in CDH1-mutant mILC, but these results were not significant when correcting for multiple testing (Table 1). CDH1-mutant mixed histology pts had lower CDH1 expression than WT pts (p<0.001, Wilcoxon rank sum exact test). PIK3CA mutations were enriched in CDH1-mutant mixed histology pts, but this difference was not statistically significant (50% vs. 31%; p=0.3, Fisher’s exact test). Log10 CDH1 expression across all mILC pts was lower than in mixed histology pts (3.01 vs 3.53; p<0.001, Wilcoxon rank-sum test). Conclusions: Our real-world dataset illustrates that the molecular landscape of CDH1-mutant mILC pts is distinct from CDH1-WT mILC pts. Additionally, mILC differs from mixed histology at a transcriptional level, with lower CDH1 expression regardless of CDH1 mutational status. Our findings suggest a use for CDH1 RNA expression levels in reclassifying mixed histology samples as mILC. Additionally, therapies targeting PIK3CA may be further investigated for their actionability in CDH1-mutant mILC cases.

Table 1.Frequency of co-mutations in CDH1-mutant vs. WT mILC cohortsGenesCDH1-mutant (n=98)CDH1 WT (n=52)p-value1q-value2n (%)n (%)PIK3CA53 (54%)6 (12%)<0.001<0.001TBX313 (13%)0 (0%)0.0040.13NCOR111 (11%)0 (0%)0.0090.21Pearson’s Chi-squared test; Fisher’sexact test. 2Falsediscovery rate correction for multiple testing

Citation Format: Andrew A Davis, Amir Behdad, Kayla Viets Layng, Firas Wehbe, Lorenzo Gerratana, Elizabeth Mauer, Alex Barrett, Ami N Shah, Paolo D’Amico, Lisa Flaum, William J Gradishar, Leonidas C Platanias, Massimo Cristofanilli. Comprehensive molecular characterization of patients with metastatic invasive lobular carcinoma (ILC): Using real-world data to describe this unique clinical entity [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 PD14-01.

Abstract PD6-08: Exploring the interplay among ESR1/PIK3CA codon variants, oncogenic pathway alterations and clinical phenotype of metastatic breast cancer (MBC) through circulating tumor DNA (ctDNA) next-generation sequencing (NGS)

Background: High throughput genomic technologies such as NGS are enhancing the ability to dynamically characterize MBC but their role in describing biological evolution of multiple mutations together remains unclear. ESR1 and PIK3CA are central mutations related to the biology and druggability of hormone-receptor positive, HER2 negative (luminal-like) MBC. The aim of this study was to explore the interplay between oncogenic pathway alterations and ESR1 and PIK3CA codon variants on the impact and clinical phenotype of luminal-like MBC. Methods: The study retrospectively analyzed a multi-institutional cohort comprising 1047 MBC patients (pts) characterized for ctDNA through NGS before treatment start at Northwestern University (Chicago, IL), Massachusetts General Hospital (Boston, MA) and Washington University in St. Louis between 2015-2020. The analysis was then focused on luminal-like MBC. Pathway classification was defined based on previous work (Sanchez-Vega F et al, Cell. 2018) (i.e., RTK, RAS, RAF, MEK, NRF2, ER, WNT, MYC, P53, cell cycle, notch, PI3K). Single nucleotide variations (SNVs) were annotated for their oncogenicity through OncoKB and ClinVar. Only pathogenic variants were included in the models. Associations among, pathway classification, and ESR1/PIK3CA codon variants were explored through stepwise logistic regression. Overall survival (OS) was tested through Cox regression. Results: The luminal-like cohort comprised 702 pts. ESR1 mutations were detected in 166 pts (24%) and PIK3CA in 214 pts (31%). The most common ESR1 gene mutations were found in codons 537 (31%), 538 (21%), 536 (8%) and 380 (7%), while alterations in codons 1047 (38%), 545 (25%), and 542 (20%) were the most common for PIK3CA. Other pathogenic SNVs were observed in 33% and 17% of pts for ESR1 and PIK3CA, respectively with the former being polyclonal. SNVs alterations were mainly observed in the PI3K (35%), P53 (32%), ER (28%), RAS (8%), RTK (8%) and cell cycle (5%) pathways, while copy number variations (CNVs) were detected in the RTK (15%), cell cycle (11%), MYC (7%) PI3K (6%) and RAF (5%) pathways. ESR1 537 variants were associated with alterations in the ER and WNT pathways, 538 with cell cycle, 380 with P53 and ER, 536 with RTK. PIK3CA 1047 variants were associated with alterations in the RTK and P53 pathways, 542 with RTK, RAS and RAF, E545 with PI3K, RAS, cell cycle and P53. 1047 and 542 were also associated with CNVs in the PI3K pathway. Independent prognostic factors in terms of OS were ESR1 537/380 codon variants (HR 1.94 P = 0.001 and HR 2.29 P = 0.047), SNVs in the RAS, cell cycle, and P53 pathways (HR 1.74 P = 0.003 HR 1.84 P = 0.009 and HR 1.56 P < 0.001) and CNVs in the cell cycle pathway (HR 1.96 P < 0.001). Conclusions: This study demonstrated how ESR1 and PIK3CA codon variants, together with alterations in specific oncogenic pathways, can differentially impact the biology and clinical phenotype of luminal-like MBC. As novel endocrine therapy agents such as selective estrogen receptor degraders (SERDs) and PI3K inhibitors are being developed, these results highlight the pivotal role of ctDNA NGS to describe tumor evolution and optimize clinical decision making.

Odds Ratio95% Confidence IntervalPESR1 Y537ER SNVs3.341.487.530.004WNT SNVs6.251.4127.740.016ESR1 D538cell cycle SNVs5.221.7915.230.003ESR1 E380P53 SNVs4.801.4116.310.012ER SNVs5.331.3321.400.018ESR1 L536RTK CNVs4.511.1517.690.031PIK3CA H1047RTK SNVs3.751.708.290.001P53 SNVs2.611.584.34< 0.001PI3K CNVs6.082.4515.08< 0.001PIK3CA E542RTK SNVs5.001.9412.880.001RAS SNVs3.651.369.770.01RAF SNVs6.011.0733.870.042PI3K CNVs6.302.2917.36< 0.001PIK3CA E545PI3K SNVs2.881.276.530.011RAS SNVs2.871.186.980.02cell cycle SNVs3.071.088.740.035NRF2 SNVs21.431.29356.520.033P53 SNVs3.752.046.89< 0.001

Citation Format: Lorenzo Gerratana, Andrew A Davis, Marko Velimirovic, Katherine Clifton, Whitney L Hensing, Ami N Shah, Charles S Dai, Carolina Reduzzi, Paolo D’Amico, Qiang Zhang, Firas Wehbe, Seth Wander, William J Gradishar, Amir Behdad, Fabio Puglisi, Cynthia X Ma, Aditya Bardia, Massimo Cristofanilli. Exploring the interplay among ESR1/PIK3CA codon variants, oncogenic pathway alterations and clinical phenotype of metastatic breast cancer (MBC) through circulating tumor DNA (ctDNA) next-generation sequencing (NGS) [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 PD6-08.

Abstract P2-08-04: Progressive metastatic breast cancer with no detectable circulating tumor DNA: Evaluating limitations of this highly sensitive tool

Background: Circulating tumor DNA (ctDNA) is being evaluated as a tool to monitor disease and guide therapy escalation and de-escalation in advanced breast cancer. The patient, disease, and treatment characteristics that influence whether tumor DNA is isolated and sequenced from the bloodstream are not well understood. We aimed to describe patient and disease characteristics of cases with undetectable ctDNA levels despite progressive metastatic breast cancer (MBC). Methods: We retrospectively identified patients (pts) with MBC who had ctDNA evaluation by the Guardant 360 assay (Redwood City, CA) as part of their routine care from 2015-2020. We correlated the ctDNA assay with the disease status at collection. We identified the patient cohort with no detectable ctDNA despite evaluation at the time of progressive disease but prior to the initiation of a new therapy (ND ctDNA/PD) and compared the clinical, pathologic, and molecular features of this group to those with detected ctDNA. Differences were tested by two proportion z-tests. Results: Of 1151 ctDNA samples collected among 473 pts with MBC, 87 (7.5%) samples had no detectable (ND) ctDNA. 54 of 87 samples with ND ctDNA were collected at a time of stable or responding disease or after a new line of therapy was started, leaving only 33 ctDNA evaluations (2.8%) among 30 pts with ND ctDNA despite collection at the time of PD prior to new therapy. Among this group there were 14 pts (47%) with HR+ HER-, 11 pts (37%) with HER2+, and 5 pts (17%) with TN MBC. This compared to 254 pts (60%) with HR+ HER2-, 82 pts (19%) with HER2+, and 85 pts (20%) with TN MBC and detectable ctDNA. HER2-positive MBC was more common in the ND ctDNA/PD group than detectable ctDNA group (p-0.02). In the ND ctDNA/PD group, the median time from MBC diagnosis to ctDNA evaluation was 7 months and pts had received a median of 0.5 prior lines of therapy for MBC. Four pts (13%) had lobular breast cancer, 24 pts (80%) had recurrent disease, 14 pts (47%) had visceral metastases, and 12 pts (40%) had oligometastatic disease. Sites of metastases at the time of ND ctDNA/PD were bone n=16 (53%), lung n=7 (23%), liver n=6 (20%), lymph node n=11 (37%), skin and soft tissue n=5 (17%), and CNS n=5 (17%). When compared to those with detectable ctDNA these differences in characteristics were not statistically significant, although numerically pts with ND ctDNA had more CNS disease (17% vs 10%) and less liver disease (20% vs 32%). At the time of ND ctDNA, the site of progression was bone n=14 (47%), CNS n=5 (17%), lymph node n=9 (30%), lung n=7 (23%), and liver n=5 (17%). There was a single site of progression in 20 pts (67%). 16 of 30 pts had repeat ctDNA analysis of which 9 pts had subsequent detectable ctDNA with a median VAF of 0.3%, a median of 1 alteration per sample, and oncogenic or likely oncogenic alterations in TP53 in 3 pts and BRCA1, CCNE1, CDH1, and PIK3CA in 1 pt each. Seven had tissue NGS, all of which showed multiple oncogenic alterations. The remaining 22 pts with ND ctDNA but no PD were responding to therapy based on imaging or had already started a new therapy since the last progression. This group also had a high proportion of HER2+ MBC (n=7, 32%) and low proportion with visceral disease (n=6, 27%) Conclusions: Although ctDNA is a highly sensitive tool to detect active MBC (<3% of samples had ND ctDNA), its sensitivity may be less in some clinical scenarios, including HER2+ MBC, when there are limited sites of progression, or when there is isolated CNS progression.

Citation Format: Ami N Shah, Lorenzo Gerratana, Shruti Chandra, Dhruvika Mukhija, Neelima Katam, Anthony K Kang, Andrew A Davis, Millen Srivastava, Saya Jacob, Paolo D'Amico, Qiang Zhang, Carolina Reduzzi, Michael Gurley, Firas Wehbe, William J Gradishar, Amir Behdad, Massimo Cristofanilli. Progressive metastatic breast cancer with no detectable circulating tumor DNA: Evaluating limitations of this highly sensitive tool [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 P2-08-04.

Abstract GS3-10: Study of samuraciclib (CT7001), a first-in-class, oral, selective inhibitor of CDK7, in combination with fulvestrant in patients with advanced hormone receptor positive HER2 negative breast cancer (HR+BC)

Background: CDK7 inhibition is a promising therapeutic strategy in cancer; acting as a regulator of the cell cycle, transcription and endocrine receptor signalling [1]. Patients with HR+BC post CDK4/6 inhibitor treatment have a poor prognosis; median progression free survival (mPFS) of ~ 8 weeks for fulvestrant post CDK4/6i in HR+BC [2,3]. Pre-clinical HR+BC models indicate the potential for synergy when the CDK7 inhibitor samuraciclib is combined with the Selective Estrogen Receptor Degrader fulvestrant [4]Materials and Methods: This single arm cohort assessed the tolerability and efficacy of samuraciclib in combination with standard dose fulvestrant in patients with advanced HR+BC; all patients had previously received an aromatase inhibitor and a CDK4/6i for advanced disease.Results: 31 patients with HR+BC received the combination of standard dose with fulvestrant and samuraciclib. 6 patients received samuraciclib dose of 240mg once daily (QD) and 25 patients a dose of 360mg QD. The combination treatment was generally well tolerated, with adverse drug reactions (AE) of note being G1-2 nausea, vomiting and diarrhoea; the majority of patients staying on treatment until disease progression.RECIST evaluation indicates evidence of reduction in tumor disease burden, including a partial response in one patient who has been on treatment for ~ 1 year.Graphic illustrations of data, including ‘waterfall’ and ‘swimmer’ plots, will be presented along with stratification data based on demographic factors such as hepatic involvement and cfDNA analysis (ESR1m, PI3Km).Conclusions: Samuraciclib has demonstrated an acceptable safety profile with evidence of anti-tumour activity in combination with fulvestrant for patients with advanced HR+BC who have progressed on their prior CDK4/6i.References:1.Patel et al., Mol Cancer Therap. 20182.Juric et al., SABCS 20183.Lindeman et al., JCO 20214.Jeselsohn et al., SABCS 2019

Citation Format: Charles Coombes, Sasha J Howell, Matthew G Krebs, Simon Lord, Laura M Kenny, Ash Bahl, Glen Clack, Edward Ainscow, Paul A Dickinson, Raluca Fostea, Janine Mansi, Carlo Palmieri, Gianflippo Bertelli, Rinath Jeselsohn, Zahi Mitri, William J Gradishar, Sagar Sardesai, Joyce O'Shaughnessy, Patrick Ward, Pavani Chalasani, Manfred Lehnert, Simak Ali, Stuart McIntosh. Study of samuraciclib (CT7001), a first-in-class, oral, selective inhibitor of CDK7, in combination with fulvestrant in patients with advanced hormone receptor positive HER2 negative breast cancer (HR+BC) [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 GS3-10.

Abstract PD14-04: Circulating tumor DNA characterization of invasive lobular carcinoma in patients with metastatic breast cancer

Background:Invasive lobular carcinoma (ILC) is the second most common histology of breast cancer, accounting for approximately 10-15% of cases. Prior studies have demonstrated that loss of E-cadherin, as well as alterations in tissue including CDH1, FOXA1, TBX3 and PTEN loss, that were more commonly observed in Luminal A ILC, while GATA3 was more commonly observed in invasive ductal carcinoma (IDC) (Ciriello et al., Cell 2015). However, data regarding the characterization of circulating tumor DNA (ctDNA) in patients (pts) with metastatic ILC are limited. We hypothesized that there would be distinct mutational profiles between pts with metastatic ILC and IDC that could be characterized using ctDNA. Methods:This retrospective cohort study included de-identified clinical, pathological, and ctDNA data from pts with metastatic breast cancer (MBC) combined under a data use agreement and approved by the institutional review boards of three sites: Washington University in St. Louis (MO), Northwestern University (Chicago, IL), and Massachusetts General Hospital (Boston, MA). All pts included in the study had ctDNA testing per standard of care with plasma-based genotyping performed by Guardant360 (Redwood City, CA) between 2015-2020. Histological classification (ILC vs. IDC) was defined based on review of pathology reports from the primary tumor or from breast biopsies of de novo MBC, and additional clinical and pathological variables were obtained via electronic medical record review. Single nucleotide variants (SNVs) were annotated using OncoKB and ClinVar and only pathogenic variants were included. Mutational profiles were compared across histologic subtypes using Fisher’s exact test to assess differences in alteration frequency across subtypes. Multivariable analysis was performed. Results:A total of 994 pts with MBC underwent ctDNA testing and were included in the analysis. 10.7% of pts had ILC (N=106) and 89.3% had IDC (N=888). 89.4% of ILC cases were categorized as hormone-receptor positive (HR+) compared with 67.1% of IDC cases. Pts with ILC had a lower frequency of triple-negative (6.7% vs. 17.7%) and HER2 positive (3.9% vs. 15.2%) breast cancer compared with IDC. Pts with ILC had a significantly higher number of pathogenic SNVs compared with IDC (mean 4.45 vs. 2.77; P=0.0037). In contrast, pts with ILC had a significantly lower number of copy number alterations as compared to pts with IDC (mean 0.40 vs. 1.03; P=0.0017). No differences were observed in mutant allele frequency between pts with ILC and IDC. The 5 most common alterations observed in pts with ILC were the following: PIK3CA, TP53, ESR1, ERBB2, and ARID1A. Alterations in AR, BRAF, CDH1, ERBB2, FGFR2, IDH2, KRAS, NF1, PIK3CA, SMAD4, and TERT were significantly higher in ILC than IDC (all P<0.05). In contrast, mutations in GATA3, and amplifications in ERBB2 and MYC were significantly more common in pts with IDC (all P<0.05). In multivariable analysis, mutations in BRAF, CDH1, ERBB2, IDH2, TERT remained significantly higher in ILC, while amplification of MYC was significantly higher in IDC (all P<0.05). After restricting the analysis to pts with HR+ HER2 negative MBC, the following genes were significant in multivariate analysis: CDH1 and ERBB2 for pts with ILC and MYC amplification for pts with IDC (all P<0.05). Discussion:In this large, multi-institutional dataset, pts with metastatic ILC were characterized by a significantly higher number of SNVs in ctDNA compared to pts with IDC, suggesting higher mutational burden. We report several alterations that were significantly different in ILC vs. IDC. These results demonstrate the ctDNA profile of pts with ILC, and future studies should explore serial plasma-based genotyping to track ILC evolution to develop targeted precision medicine based therapeutic approaches for this unique subset of pts with MBC.

Citation Format: Andrew A Davis, Lorenzo Gerratana, Katherine Clifton, Marko Velimirovic, Whitney L Hensing, Ami N Shah, Paolo D’Amico, Carolina Reduzzi, Qiang Zhang, Charles S Dai, Elyssa N Denault, Nusayba A Bagegni, Mateusz Opyrchal, Foluso O Ademuyiwa, Ron Bose, William J Gradishar, Amir Behdad, Cynthia X Ma, Aditya Bardia, Massimo Cristofanilli. Circulating tumor DNA characterization of invasive lobular carcinoma in patients with metastatic breast cancer [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 PD14-04.

Adjuvant chemotherapy in patients with invasive lobular carcinoma and use of the 21-gene recurrence score: A National Cancer Database analysis

BACKGROUND

Invasive lobular carcinoma (ILC) is traditionally considered less responsive to chemotherapy. Although the Oncotype recurrence score (RS) has been validated to identify high-risk patients who benefit from chemotherapy, some studies have questioned its relevance in patients with ILC. The objective of this study was to better characterize potential use of the RS in these patients.

METHODS

The National Cancer Database was used to identify women with stage I through III, T1 through T3, N0 or N1, hormone receptor-positive, HER2-negative ILC or invasive ductal carcinoma (IDC) who had an available RS between 2010 and 2016. Multivariable Cox regression was used to model the effect of variables on 5-year overall survival (OS). The Kaplan-Meier method was used to estimate OS according to the RS, nodal status, and chemotherapy.

RESULTS

In total, 15,763 patients with ILC and 100,070 with IDC were identified. The mean age of patients with ILC and IDC was 59.2 ± 9.1 and 57.2 ± 9.8, respectively. A lower percentage of patients with ILC versus those with IDC had a high RS, defined as >25 (6.6% vs 16.0%; P < .0001). ILC patients with a high RS who had N0 or N1 disease received approximately 10% less chemotherapy compared with similar patients who had IDC. The results indicated that the RS had statistically significant prognostic value for patients with ILC. In addition, an absolute OS advantage was correlated with the receipt of chemotherapy by patients with ILC who had a high RS with N0 or N1 disease.

CONCLUSIONS

Patients with ILC who have a high RS are treated less often with chemotherapy compared with similar patients who have IDC. Nevertheless, the RS has a prognostic as well as a predictive value in ILC, with an association between OS benefit and chemotherapy receipt in patients who have ILC with a high RS, especially if they have N1 disease.

LAY SUMMARY

Invasive lobular carcinoma (ILC) is a subtype of breast cancer comprising about 15% of cases. The Oncotype recurrence score (RS) is a genetic test of breast tumors that helps predict which patients might benefit from chemotherapy. Some have doubted the relevance of the RS for patients with ILC. In this study, the authors show that the RS is relevant for patients who have ILC. The RS has the potential of predicting the risk of recurrence and identifying patients with ILC who might benefit from chemotherapy.

Positive predictive value of ERBB2 copy number gain by tissue or circulating tumor DNA next-generation sequencing across advanced cancers

BACKGROUND

The correlation of ERBB2 copy number gain (CNG) from tissue or circulating tumor DNA (ctDNA) by next-generation sequencing (NGS) with standard HER2 tissue evaluation is not well understood.

MATERIALS AND METHODS

We retrospectively identified patients with ERBB2 CNG on commercial NGS. We described their clinical-pathologic features and calculated the positive predictive value (PPV) of ERBB2 CNG by NGS for HER2-positivity by IHC and FISH testing.

RESULTS

176 patients had NGS revealing an ERBB2 CNG (112 by tumor tissue and 91 by ctDNA). The cancer subtypes with the most cases with ERBB2 CNG by NGS were breast (n = 67), non-small cell lung (n = 25), colorectal (n = 18), gastroesophageal (n = 17), pancreatic (n = 11), and uterine (n = 11). The PPV of ERBB2 CNG in determining HER2 positivity by standard IHC/FISH definitions was 88% for tissue NGS (n = 57) and 80% for ctDNA (n = 47). The PPV among breast cancer patients for tissue NGS was 97% (n = 35) and ctDNA was 93% (n = 39). However, for non-breast cancer cases, the PPV of ERBB2 amplification by tissue NGS dropped to 76% (n = 22) and by ctDNA to 44% (n = 7).

CONCLUSIONS

ERBB2 CNG by NGS is detected in numerous malignancies for which HER2 testing is not standard. Detection of ERBB2 CNG by tissue NGS and ctDNA has a high PPV for true HER2-positivity by standard IHC and/or FISH testing in breast cancer.

Role of Fcγ receptors in HER2-targeted breast cancer therapy

Several therapeutic monoclonal antibodies (mAbs), including those targeting epidermal growth factor receptor, human epidermal growth factor receptor 2 (HER2), and CD20, mediate fragment crystallizable gamma receptor (FcγR)–dependent activities as part of their mechanism of action. These activities include induction of antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP), which are innate immune mechanisms of cancer cell elimination. FcγRs are distinguished by their affinity for the Fc fragment, cell distribution, and type of immune response they induce. Activating FcγRIIIa (CD16A) on natural killer cells plays a crucial role in mediating ADCC, and activating FcγRIIa (CD32A) and FcγRIIIa on macrophages are important for mediating ADCP. Polymorphisms in FcγRIIIa and FcγRIIa generate variants that bind to the Fc portion of antibodies with different affinities. This results in differential FcγR-mediated activities associated with differential therapeutic outcomes across multiple clinical settings, from early stage to metastatic disease, in patients with HER2+ breast cancer treated with the anti-HER2 mAb trastuzumab. Trastuzumab has, nonetheless, revolutionized HER2+ breast cancer treatment, and several HER2-directed mAbs have been developed using Fc glyco-engineering or Fc protein-engineering to enhance FcγR-mediated functions. An example of an approved anti-HER2 Fc-engineered chimeric mAb is margetuximab, which targets the same epitope as trastuzumab, but features five amino acid substitutions in the IgG 1 Fc domain that were deliberately introduced to increase binding to activating FcγRIIIa and decrease binding to inhibitory FcγRIIb (CD32B). Margetuximab enhances Fc-dependent ADCC in vitro more potently than the combination of pertuzumab (another approved mAb directed against an alternate HER2 epitope) and trastuzumab. Margetuximab administration also enhances HER2-specific B cell and T cell–mediated responses ex vivo in samples from patients treated with prior lines of HER2 antibody-based therapies. Stemming from these observations, a worthwhile future goal in the treatment of HER2+ breast cancer is to promote combinatorial approaches that better eradicate HER2+ cancer cells via enhanced immunological mechanisms.

Biomarker Analysis of the Phase III NALA Study of Neratinib + Capecitabine versus Lapatinib + Capecitabine in Patients with Previously Treated Metastatic Breast Cancer

PURPOSE

Neratinib plus capecitabine (N+C) demonstrated significant progression-free survival (PFS) benefit in NALA (NCT01808573), a randomized phase III trial comparing N+C with lapatinib + capecitabine (L+C) in 621 patients with HER2-positive (HER2+) metastatic breast cancer (MBC) who had received ≥2 prior HER2-directed regimens in the metastatic setting. We evaluated correlations between exploratory biomarkers and PFS.

PATIENTS AND METHODS

Somatic mutations were evaluated by next-generation sequencing on primary or metastatic samples. HER2 protein expression was evaluated by central IHC, H-score, and VeraTag/HERmark. p95 expression (truncated HER2) was measured by VeraTag. HRs were estimated using unstratified Cox proportional hazards models.

RESULTS

Four hundred and twenty samples had successful sequencing: 34.0% had PIK3CA mutations and 5.5% had HER2 (ERBB2) mutations. In the combined patient populations, PIK3CA mutations trended toward shorter PFS [wild-type vs. mutant, HR = 0.81; 95% confidence interval (CI), 0.64-1.03], whereas HER2 mutations trended toward longer PFS [HR = 1.69 (95% CI, 0.97-3.29)]. Higher HER2 protein expression was associated with longer PFS [IHC 3+ vs. 2+, HR = 0.67 (0.54-0.82); H-score ≥240 versus <240, HR = 0.77 (0.63-0.93); HERmark positive vs. negative, HR = 0.76 (0.59-0.98)]. Patients whose tumors had higher HER2 protein expression (any method) derived an increased benefit from N+C compared with L+C [IHC 3+, HR = 0.64 (0.51-0.81); H-score ≥ 240, HR = 0.54 (0.41-0.72); HERmark positive, HR = 0.65 (0.50-0.84)], as did patients with high p95 [p95 ≥2.8 relative fluorescence (RF)/mm2, HR = 0.66 (0.50-0.86) vs. p95 < 2.8 RF/mm2, HR = 0.91 (0.61-1.36)].

CONCLUSIONS

PIK3CA mutations were associated with shorter PFS whereas higher HER2 expression was associated with longer PFS. Higher HER2 protein expression was also associated with a greater benefit for N+C compared with L+C.

De-escalation of Endocrine Therapy in Early Hormone Receptor-positive Breast Cancer: When Is Local Treatment Enough?

OBJECTIVE

To identify subgroups of hormone receptor-positive (HR+) breast cancer patients that might not benefit from adding endocrine therapy (ET) to their local treatment.

BACKGROUND

De-escalation in breast cancer treatment has included surgery, radiation, and chemotherapy and has often focused on older patient populations. Systemic ET has yet to be de-escalated, though it carries serious side-effects, decreasing quality of life over 5 to 10 years. We hypothesize the 21-gene recurrence score (RS) could identify subgroups of younger patients whose long-term survival is unaffected by adjuvant ET.

METHODS

The National Cancer Database was used to identify women aged ≥50, with HR+, HER2-negative tumors, ≤3 cm in size, N0 status, and a RS≤25, who underwent breast-conserving surgery in 2010 to 2016. Kaplan-Meier and Cox proportional hazards models were used to identify association between treatment and overall survival (OS).

RESULTS

Of the 45,217 patients identified, 80.6% were 50 to 69 years old. 42,632 (94.3%) patients received ET and 2585 (5.7%) did not. The 5-year OS was 96.4% for patients receiving ET and 93.1% for those who did not (P < 0.001). After adjusting for all covariates, patients aged 50 to 69 with RS < 11 showed no statistically significant improvement in OS when adding ET to surgery, with or without radiation (P = 0.40). With RS 11 to 25, there was a significant improvement of OS with ET plus radiation (P < 0.001).

CONCLUSIONS

Local treatment only, with de-escalation of long-term ET, for patients aged 50 to 69 with RS < 11, seems not to impact OS and should have an anticipated quality of life improvement. Prospective studies investigating this approach are warranted.

Evaluation of the Novel 4R Oncology Care Planning Model in Breast Cancer: Impact on Patient Self-Management and Care Delivery in Safety-Net and Non-Safety-Net Centers

PURPOSE

Optimal cancer care requires patient self-management and coordinated timing and sequence of interdependent care. These are challenging, especially in safety-net settings treating underserved populations. We evaluated the 4R Oncology model (4R) of patient-facing care planning for impact on self-management and delivery of interdependent care at safety-net and non-safety-net institutions.

METHODS

Ten institutions (five safety-net and five non-safety-net) evaluated the 4R intervention from 2017 to 2020 with patients with stage 0-III breast cancer. Data on self-management and care delivery were collected via surveys and compared between the intervention cohort and the historical cohort (diagnosed before 4R launch). 4R usefulness was assessed within the intervention cohort.

RESULTS

Survey response rate was 63% (422/670) in intervention and 47% (466/992) in historical cohort. 4R usefulness was reported by 79.9% of patients receiving 4R and was higher for patients in safety-net than in non-safety-net centers (87.6%, 74.2%, P = .001). The intervention cohort measured significantly higher than historical cohort in five of seven self-management metrics, including clarity of care timing and sequence (71.3%, 55%, P < .001) and ability to manage care (78.9%, 72.1%, P = .02). Referrals to interdependent care were significantly higher in the intervention than in the historical cohort along all six metrics, including primary care consult (33.9%, 27.7%, P = .045) and flu vaccination (38.6%, 27.9%, P = .001). Referral completions were significantly higher in four of six metrics. For safety-net patients, improvements in most self-management and care delivery metrics were similar or higher than for non-safety-net patients, even after controlling for all other variables.

CONCLUSION

4R Oncology was useful to patients and significantly improved self-management and delivery of interdependent care, but gaps remain. Model enhancements and further evaluations are needed for broad adoption. Patients in safety-net settings benefited from 4R at similar or higher rates than non-safety-net patients, indicating that 4R may reduce care disparities.

Prognosis and Chemotherapy Use in Breast Cancer Patients with Multiple Lymphatic Micrometastases: An NCDB Analysis

BACKGROUND

The number of involved lymph nodes negatively affects prognosis in breast cancer patients. Nevertheless, current staging and treatment recommendations do not distinguish between patients with single versus multiple lymphatic micrometastases. In this study, we aim to better characterize these patients.

METHODS

The National Cancer Database was retrospectively queried to identify 486,800 women with stage I-III, estrogen receptor-positive/progesterone receptor-positive/human epidermal growth factor receptor 2-negative (ER+/PR+/HER2-) breast cancer and nodal status of N0, N1mi with 1 (Nmic1) or more (Nmic > 1) involved nodes, and N1 with 1 involved node (N1.1), from 2010 to 2016. Patients with different nodal statuses were compared regarding treatment characteristics, survival, and benefit from chemotherapy by their 21-gene recurrence score (RS).

RESULTS

Of the 23,072 N1mi patients, 88.3% were Nmic1 and 11.7% were Nmic > 1. Nmic > 1 patients were younger, had larger and higher-grade tumors, with more lymphovascular invasion, and were more commonly treated by axillary dissection, radiation, and chemotherapy than Nmic1 patients. In that, they were comparable with N1.1 patients. Five-year survival of Nmic > 1 patients (88.1%) was worse than Nmic1 patients (90.1%; p = 0.02), but similar to N1.1 patients (87.9%). Nmic1, Nmic > 1, and N1.1 patients with RS 11-25 exhibited a < 2% absolute survival benefit associated with chemotherapy. With RS > 25, Nmic > 1 patients showed a 3.5% benefit, similar to Nmic1 (4.8%) and lower than N1.1 (10.9%) patients.

CONCLUSIONS

Nmic > 1 breast cancer patients have worse prognoses than Nmic1 patients, similar to N1.1 patients. Our data suggest those patients with RS 11-25 have minimal benefit from chemotherapy. These findings should be taken into account when discussing prognosis and considering chemotherapy in patients with lymphatic micrometastases.

Updates in HER2-Positive and Triple-Negative Breast Cancers

The recent approval of 4 agents for the treatment of patients with metastatic HER2-positive breast cancer has led to expanded recommendations in the NCCN Guidelines for treatment of this disease. For triple-negative disease, immunotherapy continues to gain traction in this challenging subtype, both in the preoperative and metastatic settings, though not yet as adjuvant treatment. Sacituzumab govitecan is another new agent with strong utility in triple-negative disease, and PARP inhibitors are recommended options in BRCA-mutated disease.

NCCN Guidelines® Insights: Breast Cancer, Version 4.2021

The NCCN Guidelines for Breast Cancer include up-to-date guidelines for clinical management of patients with carcinoma in situ, invasive breast cancer, Paget disease, phyllodes tumor, inflammatory breast cancer, male breast cancer, and breast cancer during pregnancy. These guidelines are developed by a multidisciplinary panel of representatives from NCCN Member Institutions with breast cancer-focused expertise in the fields of medical oncology, surgical oncology, radiation oncology, pathology, reconstructive surgery, and patient advocacy. These NCCN Guidelines Insights focus on the most recent updates to recommendations for adjuvant systemic therapy in patients with nonmetastatic, early-stage, hormone receptor-positive, HER2-negative breast cancer.

Efficacy of Margetuximab vs Trastuzumab in Patients With Pretreated ERBB2-Positive Advanced Breast Cancer: A Phase 3 Randomized Clinical Trial

Question

Does margetuximab plus chemotherapy prolong progression-free survival and/or overall survival of patients with pretreated ERBB2-positive advanced breast cancer, relative to trastuzumab plus chemotherapy?

Findings

In the SOPHIA phase 3 randomized clinical trial of 536 patients with pretreated ERBB2-positive advanced breast cancer, margetuximab plus chemotherapy generated a statistically significant 24% relative risk reduction in the hazard of progression vs trastuzumab plus chemotherapy. After the second planned interim analysis of 270 deaths, median OS was 21.6 months with margetuximab vs 19.8 months with trastuzumab, and final analysis of OS will be reported subsequently.

Meaning

This trial demonstrates a head-to-head advantage of margetuximab (an Fc-engineered ERBB2-targeted antibody) compared with trastuzumab in a pretreated ERBB2-positive advanced breast cancer population.

Importance

ERRB2 (formerly HER2)–positive advanced breast cancer (ABC) remains typically incurable with optimal treatment undefined in later lines of therapy. The chimeric antibody margetuximab shares ERBB2 specificity with trastuzumab but incorporates an engineered Fc region to increase immune activation.

Objective

To compare the clinical efficacy of margetuximab vs trastuzumab, each with chemotherapy, in patients with pretreated ERBB2-positive ABC.

Design, Setting, and Participants

The SOPHIA phase 3 randomized open-label trial of margetuximab plus chemotherapy vs trastuzumab plus chemotherapy enrolled 536 patients from August 26, 2015, to October 10, 2018, at 166 sites in 17 countries. Eligible patients had disease progression on 2 or more prior anti-ERBB2 therapies and 1 to 3 lines of therapy for metastatic disease. Data were analyzed from February 2019 to October 2019.

Interventions

Investigators selected chemotherapy before 1:1 randomization to margetuximab, 15 mg/kg, or trastuzumab, 6 mg/kg (loading dose, 8 mg/kg), each in 3-week cycles. Stratification factors were metastatic sites (≤2, >2), lines of therapy (≤2, >2), and chemotherapy choice.

Main Outcomes and Measures

Sequential primary end points were progression-free survival (PFS) by central blinded analysis and overall survival (OS). All α was allocated to PFS, followed by OS. Secondary end points were investigator-assessed PFS and objective response rate by central blinded analysis.

Results

A total of 536 patients were randomized to receive margetuximab (n = 266) or trastuzumab (n = 270). The median age was 56 (27-86) years; 266 (100%) women were in the margetuximab group, while 267 (98.9%) women were in the trastuzumab group. Groups were balanced. All but 1 patient had received prior pertuzumab, and 489 (91.2%) had received prior ado-trastuzumab emtansine. Margetuximab improved primary PFS over trastuzumab with 24% relative risk reduction (hazard ratio [HR], 0.76; 95% CI, 0.59-0.98; P = .03; median, 5.8 [95% CI, 5.5-7.0] months vs 4.9 [95% CI, 4.2-5.6] months; October 10, 2018). After the second planned interim analysis of 270 deaths, median OS was 21.6 months with margetuximab vs 19.8 months with trastuzumab (HR, 0.89; 95% CI, 0.69-1.13; P = .33; September 10, 2019), and investigator-assessed PFS showed 29% relative risk reduction favoring margetuximab (HR, 0.71; 95% CI, 0.58-0.86; P < .001; median, 5.7 vs 4.4 months; September 10, 2019). Margetuximab improved objective response rate over trastuzumab: 22% vs 16% (P = .06; October 10, 2018), and 25% vs 14% (P < .001; September 10, 2019). Incidence of infusion-related reactions, mostly in cycle 1, was higher with margetuximab (35 [13.3%] vs 9 [3.4%]); otherwise, safety was comparable.

Conclusions and Relevance

In this phase 3 randomized clinical trial, margetuximab plus chemotherapy had acceptable safety and a statistically significant improvement in PFS compared with trastuzumab plus chemotherapy in ERBB2-positive ABC after progression on 2 or more prior anti-ERBB2 therapies. Final OS analysis is expected in 2021.

Trial Registration

ClinicalTrials.gov Identifier: NCT02492711

Abstract PS2-08: Identification of incidental putative germline variants in circulating tumor DNA

Background: Circulating tumor DNA (ctDNA) has emerged as a potential tool for detecting disease recurrence, monitoring response to therapy, and identifying resistance mutations in the peripheral blood. With increased frequency of testing, there is an unmet need to recognize putative germline variants in ctDNA, and the probability that these variants are associated with inherited conditions. Here, we evaluated a large cohort of breast cancer patients who underwent ctDNA evaluation to determine the type and frequency of ctDNA mutations identified with confirmed germline testing.

Methods: We reviewed ctDNA testing from a single institution (Northwestern University). All breast cancer patients who had next-generation sequencing (NGS) performed by Guardant Health (Redwood City, CA) from 2015-2020 were included in this retrospective study. An allele frequency cutoff of 30% was pre-established as a threshold to review patient charts to determine whether genetic counseling and germline testing were performed, along with the timeframe of this testing (e.g. before or after ctDNA evaluation). Clinical information including demographics, pathology, tissue NGS testing, and germline testing were collected. Descriptive analyses and statistical associations were performed using STATA.

Results: The initial cohort consisted of 520 patients with breast cancer who underwent ctDNA testing. From this, we identified 84 patients (16.2%) who had at least one variant with allele frequency ≥30%. The most common variants identified were the following: TP53 (34%), PIK3CA (27%), BRCA1 (9%), BRCA2 (8%), and AKT1 (4%). Guardant360 classified 99% of these variants as pathogenic and 1% as a variant of unknown significance. Germline positivity using a separate CLIA-approved test for this indication was confirmed at the following frequencies: BRCA1 (2 of 8 positive, 25%), BRCA2 (2 of 5 positive, 40%), PIK3CA (0 of 5 positive), and TP53 (0 of 26 positive). In total, 14% of patients with ctDNA allele frequency ≥30% had a confirmed germline mutation. Lower age at breast cancer diagnosis was significantly associated with the probability of germline testing prior to ctDNA evaluation (P=0.0001). For patients who had a variant with allele frequency ≥30%, 24.3% never received genetic counseling or germline testing.

Conclusion: High allele frequency ctDNA variants (≥30%) were present in 16% of patients who underwent ctDNA evaluation with 14% of these variants confirmed as true germline variants. Consenting patients for ctDNA testing should include the possibility of identifying putative germline variants, and criteria should be established to refer patients for subsequent genetic counseling and germline testing, given the potential implications for patients and their family members.

Citation Format: Andrew A Davis, Michael C Burns, Lorenzo Gerratana, Paolo D'Amico, Saya Jacob, Ami Shah, Neelima Katam, Firas Wehbe, Qiang Zhang, Elena Vagia, Lisa Flaum, Kalliopi P. Siziopikou, Leonidas C Platanias, Amir Behdad, William J Gradishar, Massimo Cristofanilli. Identification of incidental putative germline variants in circulating tumor DNA [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 PS2-08.

Abstract PS10-12: Integrated safety summary of single agent and combination margetuximab in phase 1, 2, and 3 studies of HER2-positive advanced cancers and metastatic breast cancer (MBC)

Background Margetuximab (M) is an investigational Fc-engineered anti-HER2 monoclonal antibody that targets the same epitope as trastuzumab (T). Compared with T, M has higher affinity for both the 158V (high-binding) and 158F (low-binding) allotypes of the activating Fc receptor CD16A. M enhances innate immunity more effectively than T in vitro, including CD16A-mediated antibody-dependent cellular cytotoxicity. Samples collected from patients (pts) before and after single-agent treatment also demonstrate that M induces HER2-specific adaptive immune responses, including both T- and B-cell responses. The SOPHIA trial (NCT02492711) in pts with pretreated HER2+ MBC showed that M+chemotherapy (chemo) improved progression-free survival vs T+chemo, with comparable safety. A pooled analysis of M safety across 3 clinical trials is presented. Methods Study 01 (NCT01148849), an ongoing Phase 1 dose-finding/safety study of M monotherapy, enrolled 66 pts with advanced HER2+ carcinomas, including 27 with MBC. Study 02 (NCT01828021), a completed Phase 2 study of M monotherapy in low-expressing HER2+ MBC, enrolled 25 pts. Study 04 (NCT02492711), an ongoing Phase 3 study in pts with pretreated HER2+ MBC to compare M + chemo vs T + chemo, randomized 536 pts, of whom 264 and 265 received M and T, respectively. The pooled safety population includes all pts who received any M in Study 01 (cutoff 01Oct2015), Study 02 (cutoff 02Aug2017), and Study 04 (cutoff 10OCT2018). Treatment-emergent adverse events (AEs), defined as AEs that began or worsened in severity on or after first dose of study drug through an End of Treatment Visit or 28 days after last study treatment, are reported. Results Of 355 pts that received at least 1 dose of M, 295 received 15 mg/kg Q3W, and 60 received other doses from 0.1 - 18 mg/kg. Median (mean, range) number of cycles for all dose levels was 5.0 (6.6, 1-43), higher on Study 04 (6.0) than Study 01 (1-3 across dose groups) or Study 02 (2.0). Most pts (347 [97.7%]) experienced at least 1 AE, and about half (173 [48.7%]) had at least 1 Grade &gt;/= 3 AE. Serious AE (SAE) incidence across studies was low (58 [16.3%]), and 21 pts (5.9%) discontinued M due to AEs. Most frequently reported AEs (&gt;/= 20%) were fatigue (124 [34.9]), nausea (103 [29.0%]), diarrhea (75 [21.1%]), and neutropenia (75 [21.1%]). Blood/lymphatic system disorders were the most frequent events by SOC, and largely restricted to Study 04. Increased neutropenia on M (26.1%), relative to T (20.4%), was observed in Study 04 yet both febrile neutropenia (M 3.0%, T 4.5%) and infections (M 36.4%, T 39.6%) were higher on T. By contrast, Study 01 and Study 02 revealed no tendency of M monotherapy to cause neutropenia. Overall, infusion related reactions (IRRs) were observed in 51 pts (14.4%), primarly at first infusion, including serious IRRs in 5 (1.4%). Also, 34 pts (9.6%) had &gt; 15% reduction in LVEF with a median time to &gt; 15% reduction of 49 days. In all pts with complete follow-up, these LVEF reductions were asymptomatic and reversible. No M-induced cardiac conduction abnormalities were noted. In Study 04, similar proportions in both groups experienced AEs (M 97.7%, T 96.2%), including Grade &gt;/= 3 AEs (M 52.3%, T 48.3%), SAEs (M 14.8%, T 17.4%), discontinuations due to AEs (M 3.0%, T 2.6%), and deaths due to AEs (M 0.8%, T 0.8%). As of the 23Feb2020 safety update, 2 pts remain on M in Study 01, after 116 and 109 cycles (6.7 and 6.3 years), respectively. In Study 04, 16 pts (6%) continued on M, and 7 (2.6%) remained on T. Discussion M has demonstrated an acceptable safety profile across Phase 1, 2, and 3 studies. It has been administered for over 6 years without long-term cumulative safety issues. Combined M plus chemotherapy Q3W demonstrated acceptable safety and tolerability, similar to that for T plus chemotherapy Q3W in Study 04.

Citation Format: Seock-Ah Im, Fatima Cardoso, Javier Cortes, Giuseppe Curigliano, Mark D. Pegram, Hope S. Rugo, Ursa Brown-Glaberman, Denise A. Yardley, Sung-Bae Kim, Maaike de Boer, Zbigniew Nowecki, Vesna Glavicic, Ido Wolf, Nele Claes, Joo Hyuk Sohn, Thomas Bachelot, Peter A. Kaufman, Jan Baughman, Shengyan Hong, Kenneth Jacobs, Edwin Rock, William J. Gradishar. Integrated safety summary of single agent and combination margetuximab in phase 1, 2, and 3 studies of HER2-positive advanced cancers and metastatic breast cancer (MBC) [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 PS10-12.

Abstract PS2-33: Investigating oncogenic signaling pathways in inflammatory metastatic breast cancer (MBC) though circulating tumor DNA (ctDNA) next-generation sequencing (NGS)

Background: Inflammatory breast cancer (IBC) has a distinctive and aggressive clinical behavior but its underlying biological characteristics have not been fully elucidated. The extended analysis of somatic alterations in The Cancer Genome Atlas (TCGA) highlighted canonical oncogenic pathways that were consistently represented across different tumor subtypes. The aim of this study was to translate such pathway-based characterization to the clinical setting through ctDNA NGS to dissect IBC’s biology and prognosis.

Methods: The study retrospectively analyzed 255 metastatic breast cancer (MBC) patients (pts) treated and characterized for ctDNA at Northwestern University (Chicago, IL). ctDNA was analyzed using the Guardant360 NGS assay (Guardant Health). Only non-synonymous alterations were analyzed. Pathway classification was defined based on prior work (Sanchez-Vega F et al, Cell. 2018). Associations among clinical characteristics, pathway classification, and IBC were explored through uni- and multivariate logistic regression; survival was tested though uni- and multivariate Cox regression both for progression-free survival (PFS) and overall survival (OS).

Results: Of 255 enrolled pts, 124 (48%) were diagnosed with hormone receptor positive (HR pos) MBC, 75 (30%) with HER2-positive (HER2_pos) MBC and 56 (22%) with triple negative (TNBC) MBC. IBC was diagnosed in 74 pts (30%). Receptor-tyrosine kinase, RTK (130 pts, 51%), p53 (130 pts, 51%), PI3K/Akt (116 pts, 46%), and cell cycle (91 pts, 36%) were the most often altered pathways. The multivariate model highlighted the association of IBC with HER2_pos (OR: 2.19; 95%CI: 1.09 - 4.38; P=0.0276), an increased number of alterations in the p53 pathway (OR: 2.05; 95%CI: 1.12 - 3.75; P=0.0197) and a decreased number of alterations in the RAS pathway (OR: 0.34; 95%CI: 0.14 - 0.80; P=0.0137). Decreased alterations in the ER pathway were borderline significant (OR: 0.48; 95%CI: 0.22 - 1.03; P=0.0584). Only cell cycle alterations had an impact on PFS for IBC (HR: 2.20; 95%CI: 1.18 - 4.08; P=0.0127), while p53 and Wnt had an impact on nonIBC (respectively HR: 2.00; 95%CI: 1.23 - 3.25; P=0.0052 and HR: 3.40; 95%CI: 1.20 - 9.64; P=0.0212). The univariate model showed a significant impact on OS RAF, ER, and cell cycle pathways alterations for IBC, the role of ER and cell cycle pathways alterations was confirmed in the multivariate model (respectively HR: 6.19; 95%CI: 1.63 - 23.48; P=0.0073 and HR: 3.79; 95%CI: 1.04 - 13.75; P=0.0431). The multivariate model showed a prognostic impact only for p53 in the nonIBC subgroup (HR: 2.20; 95%CI: 1.11 - 4.36; P=0.0237)

Conclusion: The ctDNA-based oncogenic signaling pathway characterization showed different biological and prognostic features across IBC and nonIBC MBC patients. Alterations of the p53 pathway were more likely to be present in IBC pts, while alterations in the RAS pathway were less represented in this cohort. ER and cell cycle pathways’ alterations impacted the OS of IBC MBC patients. Although preliminary, these results suggest a more comprehensive biological characterization based on ctDNA for treatment selection and clinical decision-making.

Main alterations and pathwayGeneNumber of alterations%PathwayTP5318815.58p53PIK3CA14111.68PI3K/AktERBB2725.97RTKESR1705.8ERMYC574.72MycFGFR1463.81RTKEGFR453.73RTKCCNE1383.15Cell cycleMET322.65RTKNF1322.65RAS

Citation Format: Lorenzo Gerratana, Andrew A Davis, Marco Mina, Saya L Jacob, Qiang Zhang, Ami N Shah, Paolo D’Amico, Neelima Katam, Firas Wehbe, Elena Vagia, Lisa Flaum, Leonidas Platanias, Amir Behdad, Fabio Puglisi, William J Gradishar, Giovanni Ciriello, Massimo Cristofanilli. Investigating oncogenic signaling pathways in inflammatory metastatic breast cancer (MBC) though circulating tumor DNA (ctDNA) next-generation sequencing (NGS) [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 PS2-33.

The Global Landscape of Treatment Standards for Breast Cancer

Background

Breast cancer (BC) is a leading cause of morbidity, mortality, and disability for women worldwide. There is substantial variation in treatment outcomes, which is function of multiple variables, including access to treatment. Treatment standards can promote quality and improve survival; thus, their development should be a priority for the cancer-control planning.

Methods

We extracted the guidelines for the treatment of BC from a systematic review of the literature. We evaluated the development process, the methodology, and the recommendations formulated and surveyed the country resource stratification. Metrics of health-system capacity were selected to study the guidelines context appropriateness.

Results

We analyzed 49 distinct guidelines for BC, mostly in English language (n = 23), developed in upper-middle and high-income countries of the European and American regions (n = 39). A resource-stratified approach was identified in a quarter of the guidelines (n = 11), mostly from resource-constrained settings. Only one-half of the guidelines reached a gender balance of the authorship, and 10.2% were based on a multidisciplinary steering committee. A number of efforts and solutions of resource adaptations were recognized, mostly in low- and middle-income countries. Overall, the national guidelines appeared not sensitive enough of the local health-system capacity in formulating recommendations, with possible exception for the radiation therapy availability.

Conclusion

This global landscape of treatment standards for BC demonstrates that the majority is not context appropriate. Research on the formulation of cancer treatment standards is highly warranted, along with novel platforms for developing and disseminating resource-appropriate guidance.

Phase III, Randomized Study of Dual Human Epidermal Growth Factor Receptor 2 (HER2) Blockade With Lapatinib Plus Trastuzumab in Combination With an Aromatase Inhibitor in Postmenopausal Women With HER2-Positive, Hormone Receptor–Positive Metastatic Breast Cancer: Updated Results of ALTERNATIVE

PURPOSE

Human epidermal growth factor receptor 2 (HER2) targeting plus endocrine therapy (ET) improved clinical benefit in HER2-positive, hormone receptor (HR)–positive metastatic breast cancer (MBC) versus ET alone. Dual HER2 blockade enhances clinical benefit versus single HER2 blockade. The ALTERNATIVE study evaluated the efficacy and safety of dual HER2 blockade plus aromatase inhibitor (AI) in postmenopausal women with HER2-positive/HR-positive MBC who received prior ET and prior neo(adjuvant)/first-line trastuzumab (TRAS) plus chemotherapy. This updated article reflects minor numerical corrections in some secondary efficacy analyses that resulted from programming errors and that do not change the major conclusions of the study.

METHODS

Patients were randomly assigned (1:1:1) to receive lapatinib (LAP) plus TRAS plus AI, TRAS plus AI, or LAP plus AI. Patients for whom chemotherapy was intended were excluded. The primary end point was progression-free survival (PFS; investigator assessed) with LAP plus TRAS plus AI versus TRAS plus AI. Secondary end points were PFS (comparison of other arms), overall survival (OS), overall response rate (ORR), clinical benefit rate (CBR), and safety.

RESULTS

Three hundred fifty-five patients were included in this analysis: LAP plus TRAS plus AI (n = 120), TRAS plus AI (n = 117), and LAP plus AI (n = 118). Baseline characteristics were balanced. The study met its primary end point; superior PFS was observed with LAP plus TRAS plus AI versus TRAS plus AI (median PFS, 11 v 5.6 months; hazard ratio, 0.62 [95% CI, 0.45 to 0.88]; P = .0063). A consistent PFS benefit was observed in predefined subgroups. ORR, CBR, and OS also favored LAP plus TRAS plus AI. The median PFS with LAP plus AI versus TRAS plus AI was 8.3 versus 5.6 months (hazard ratio, 0.85 [95% CI, 0.62 to 1.17]; P = .3159). Common adverse events (AEs; ≥ 15%) with LAP plus TRAS plus AI, TRAS plus AI, and LAP plus AI were diarrhea (69%, 9%, and 51%, respectively), rash (36%, 2%, and 28%, respectively), nausea (22%, 9%, and 22%, respectively), and paronychia (30%, 0%, and 15%, respectively), mostly grade 1 or 2. Serious AEs were reported similarly across the 3 groups, and AEs leading to discontinuation were lower with LAP plus TRAS plus AI.

CONCLUSION

Dual HER2 blockade with LAP plus TRAS plus AI showed superior PFS benefit versus TRAS plus AI in patients with HER2-positive/HR-positive MBC. This combination offers an effective and safe chemotherapy-sparing alternative treatment regimen for this patient population.

The Use of Serial Circulating Tumor DNA to Detect Resistance Alterations in Progressive Metastatic Breast Cancer

PURPOSE

Circulating tumor DNA (ctDNA) is a promising tool for noninvasive longitudinal monitoring of genomic alterations. We analyzed serial ctDNA to characterize genomic evolution in progressive metastatic breast cancer.

EXPERIMENTAL DESIGN

This was a retrospective cohort between 2015 and 2019 obtained under an Institutional Review Board-approved protocol at Northwestern University (Chicago, IL). ctDNA samples were analyzed with Guardant360 next-generation sequencing (NGS) assay. A total of 86 patients had at least two serial ctDNA collections with the second drawn at first post-NGS progression (PN1) by imaging and clinical assessment. A total of 27 participants had ctDNA drawn at second post-NGS clinical progression (PN2). We analyzed alterations, mutant allele frequency (MAF), number of alterations (NOA), and sites of disease on imaging in close proximity to ctDNA evaluation. Matched pairs' variations in MAF, NOA, and alterations at progression were tested through Wilcoxon test. We identified an independent control cohort at Massachusetts General Hospital (Boston, MA) of 63 patients with serial ctDNA sampling and no evidence of progression.

RESULTS

We identified 44 hormone receptor-positive, 20 HER2⁺, and 22 triple-negative breast cancer cases. The significant alterations observed between baseline and PN1 were TP53 (P < 0.0075), PIK3CA (P < 0.0126), AR (P < 0.0126), FGFR1 (P < 0.0455), and ESR1 (P < 0.0143). Paired analyses revealed increased MAF and NOA from baseline to PN1 (P = 0.0026, and P < 0.0001, respectively). When compared with controls without progression, patients with ctDNA collection at times of progression were associated with increased MAF and NOA (P = 0.0042 and P < 0.0001, respectively).

CONCLUSIONS

Serial ctDNA testing identified resistance alterations and increased NOA and MAF were associated with disease progression. Prospective longitudinal ctDNA evaluation could potentially monitor tumor genomic evolution.

The 21-gene recurrence score in node-positive, hormone receptor-positive, HER2-negative breast cancer: a cautionary tale from an NCDB analysis

PURPOSE

The 21-gene recurrence score assay (RS) has not been prospectively validated to predict adjuvant chemotherapy benefit in hormone receptor-positive (HR+), HER2-negative (HER2-), node-positive breast cancer patients. Nevertheless, de-escalation based on RS has been demonstrated and partially advocated by retrospective data. The purpose of this study was to identify subgroups of node-positive patients with low to intermediate RS who still benefit from adjuvant chemotherapy.

METHODS

The National Cancer Database was used to identify 28,591 women with stage I-III, T1-T3, N1, HR+, HER2- breast cancer and a RS ≤ 25 between 2010 and 2016. Univariate and multivariate analyses were used to identify variables correlating with chemotherapy use and 5-year survival. Subgroup analysis was performed to discern patients in whom the use of adjuvant chemotherapy correlated with better survival.

RESULTS

A 35% decline in chemotherapy use was observed from 2010 to 2016. Patients with younger age, higher RS, larger tumors and more positive lymph nodes, and those treated by mastectomy, axillary lymph node dissection and radiation, were more likely to receive chemotherapy. Chemotherapy use was associated with an improved 5-year survival (HR = 1.63, 95% CI 1.28-2.07). Upon subgroup analysis, this association was lost in patients > 70 years and those with a RS ≤ 11, while patients ≤ 70 with a RS of 12-25 treated with chemotherapy had an absolute 5-year survival advantage of 3.0% (HR = 1.91, 95% CI 1.42-2.57).

CONCLUSION

Clinicians should be cautious when considering omission of adjuvant chemotherapy in patients ≤ 70 years, with HR+, HER2-, N1 tumors and a RS 12-25, at least until the results of the anticipated RxPONDER trial become available.

NCCN Guidelines Updates: Breast Cancer

Advances in molecular testing have ushered in the new era of precision medicine. The 2018 publication of the TAILORx trial helped refine the use of genetic expression assays, specifically the 21-gene recurrence score, in assigning patients to endocrine therapy alone or with chemotherapy. The NCCN Guidelines for Breast Cancer explore the clinical applications of this study. The algorithm for managing the axilla in early breast cancer has been further refined, based on the presence or absence of clinical evidence of lymph node involvement. Ovarian suppression has been validated as the optimal approach in higher risk premenopausal women, based on updated analysis of the SOFT and TEXT pivotal trials. In the metastatic setting, the NCCN Guidelines further reinforce the benefit of the CDK4/6 inhibitors, extending the "preferred" recommendation to all the available agents in metastatic disease. Options in triple-negative breast cancer now include, for the first time, an immunotherapeutic agent.

Landscape of circulating tumour DNA in metastatic breast cancer

BACKGROUND

We describe the genomic landscape of circulating tumour DNA (ctDNA) across pathological subtypes of metastatic breast cancer.

METHODS

255 clinically annotated patients with ctDNA testing by Guardant360 were stratified into HR+, HER2+, and TNBC cohorts. Frequency and heterogeneity of alterations were reported. Paired ctDNA and tissue sequencing were compared for a subset of patients. The association of ctDNA and metastatic sites of disease on imaging was also assessed.

FINDINGS

89% of patients had at least one ctDNA alteration detected. The most common single nucleotide variants (SNVs) for HR+ patients were PIK3CA, ESR1, and TP53. For HER2+, these were TP53, PIK3CA, and ERBB2 with ERBB2 as the most frequent copy number variant (CNV). For TNBC, the most common SNVs were TP53 and PIK3CA, and the most frequent CNVs were MYC, CCNE1, and PIK3CA. TNBC patients had a significantly higher mutant allele frequency (MAF) of the highest variant compared to HR+ or HER2+ patients (P<0.05). Overall, alterations in PIK3CA, ESR1, and ERBB2 were observed in 39.6%, 16.5%, and 21.6% of patients, respectively. Agreement between blood and tissue was 79-91%. MAF and number of alterations were significantly associated with number of metastatic sites on imaging (P<0.0001).

INTERPRETATION

These data demonstrate the genetic heterogeneity of metastatic breast cancer in blood, the high prevalence of clinically actionable alterations, and the potential to utilise ctDNA as a surrogate for tumour burden on imaging.

FUNDING

Lynn Sage Cancer Research Foundation, OncoSET Precision Medicine Program, and REDCap support was funded by the National Institutes of Health UL1TR001422.

NCCN Guidelines Insights: Breast Cancer, Version 3.2018

These NCCN Guidelines Insights highlight the updated recommendations for use of multigene assays to guide decisions on adjuvant systemic chemotherapy therapy for women with hormone receptor-positive, HER2-negative early-stage invasive breast cancer. This report summarizes these updates and discusses the rationale behind them.

Practice-Changing Interventions in the Systemic Management of Breast Cancer

Systemic treatment for metastatic breast cancer now incorporates many targeted agents and a plethora of combinations specific to the breast cancer subtype. New to the treatment paradigm are fam-trastuzumab deruxtecan-nxki, and tucatinib for HER2-positive disease; the PI3K inhibitor alpelisib in combination with fulvestrant for estrogen receptor–positive and PIK3CA-mutated tumors; PARP inhibitors for patients with germline BRCA1/2 mutations; and the anti–PD-L1 agent atezolizumab in combination with albumin-bound paclitaxel for triple-negative disease with PD-L1 mutations in tumors. In addition, for estrogen receptor–positive disease, the role of CDK4/6 inhibitors increased substantially during the past year, as overall survival results have emerged. These targeted agents are greatly improving patient outcomes, and thus have all been incorporated into the NCCN Guidelines for Breast Cancer.

Novel Neoadjuvant Treatment Strategies for Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC), which accounts for approximately 10% to 15% of breast cancers, remains the most aggressive subtype and is characterized by early disease relapse for a subset of patients. TNBC remains a clinical challenge, given the lack of effective targeted treatments such as endocrine therapy for hormone receptor-positive (HR+) tumors or therapies against HER2.

Breast Cancer, Version 3.2020, NCCN Clinical Practice Guidelines in Oncology

Several new systemic therapy options have become available for patients with metastatic breast cancer, which have led to improvements in survival. In addition to patient and clinical factors, the treatment selection primarily depends on the tumor biology (hormone-receptor status and HER2-status). The NCCN Guidelines specific to the workup and treatment of patients with recurrent/stage IV breast cancer are discussed in this article.

Abstract PD8-03: Clinico-pathological and molecular features in young women with metastatic breast cancer

Introduction: Advanced breast cancer can be more aggressive and portend a worse prognosis in the younger population (age &lt; 50). While several studies have outlined clinico-pathologic features and molecular features of primary disease in young women with breast cancer, data in the metastatic setting remain scarce. Thus, the goal of this study was to explore the underlying clinic-pathologic and molecular profile of young women with metastatic breast cancer.

Methods: We conducted a retrospective analysis of 138 females with metastatic breast cancer treated at Northwestern Medicine who provided consent for serial evaluation of circulating biomarkers. Patient were divided into two cohorts based on age at the time of metastasis, namely premenopausal (defined as age &lt; 50) and postmenopausal (age ≥ 50). CellSearch™ immunomagnetic kit (Menarini Silicon Biosystems) was utilized to enumerate circulating tumor cells (CTCs), and the CellSearch™ CXC Kit (in 7.5 cc whole blood) characterized CTC HER2 expression. Circulating tumor DNA (ctDNA) was sequenced using the Guardant360 next-generation sequencing (NGS) assay (Guardant Health). When available, tissue samples from the primary and metastatic site(s) were sequenced using FoundationOne and/or Tempus xT NGS assays. Associations were drawn using Pearson’s χ2 test, independent samples T-tests, and multivariate logistic regression.

Results: Of the 138 women, 54 (39%) were premenopausal with median age of 42 (range: 28-49), and 84 (61%) were postmenopausal with median age of 57 (range: 50-81). For the premenopausal cohort, 96% had invasive ductal carcinoma, 2% invasive lobular carcinoma and 2% mixed/unknown, compared to postmenopausal with 74%, 19% and 7% respectively, p=0.003. No statistically significant association was observed based on disease subtype (HR+/HER2-, HR+/HER2+, HR-/HER2+, TNBC), correspondingly stratified as 46%, 17%, 9%, 28% (premenopausal) and 57%, 10%, 13% 20% (postmenopausal). In total, 39% of the premenopausal and 40% of the postmenopausal patients had inflammatory breast cancer (IBC). Among patients initially diagnosed with non-metastatic disease, time (years) to metastasis was 2.76 (95% CI 2.11 to 3.41) for the premenopausal and 6.08 (95% CI 4.89 to 7.27) for the postmenopausal cohort, p=0.0001. Statistically significant associations were found when comparing the NGS datasets, derived from serial collection of ctDNA +/- tissue samples. Specifically, the premenopausal group had a higher incidence of GATA3 (11 vs 6 cases; p=0.017) alterations, but a lower incidence of NF1 (1 vs 18; p&lt;0.001) and RB1 (1 vs 9; p=0.049) alterations. Most common gene alterations included TP53 (67%), PIK3CA (45%), ERBB2 (26%), GATA3 (26%), MYC (24%), FGFR1 (19%) and ESR1 (17%) for the younger cohort, versus TP53(67%), PIK3CA (39%), ESR1 (27%), NF1 (27%), MYC (23%), ERBB2 (23%) and FGFR1 (20%) for the postmenopausal cohort. There were no statistically significant differences between the cohorts in terms of total number of ctDNA alterations at baseline draw (median[IQR]: 3[1-7] premenopausal group; 5[2-7] postmenopausal group), presence of ≥5 CTCs (54%; 46% of total cases, respectively), occurrence of CTC clusters (26%; 24%), or HER2+ CTC expression (44%; 45%).

Conclusion: Our data reveal that premenopausal women diagnosed with metastatic breast cancer had a more rapid progression to metastasis and differ from their postmenopausal counterparts in both their pathologic profile (almost exclusively invasive ductal carcinoma) and molecular profile (notably, gene alteration frequencies of NF1, RB1 and GATA3), which could have significant implications in developing targeted treatment paradigms for younger women. Additionally, CTC prevalence in the metastatic setting differs from earlier stage breast cancer data showing a higher proportion of ≥5 CTCs in postmenopausal patients.

Citation Format: Kristen Carroll, Ami M Shah, Lorenzo Gerratana, Chenyu Lin, Andrew A Davis, Qiang Zhang, Youbin Zhang, Lisa Flaum, Amir Behdad, Leonidas C Platanias, William J Gradishar, Massimo Cristofanilli. Clinico-pathological and molecular features in young women with metastatic 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 PD8-03.

Abstract P5-01-10: Next generation sequencing-based gene variant-oriented characterization in metastatic breast cancer: An innovative analysis using ctDNA

Introduction: Novel high throughput genomic technologies are enhancing the ability to dynamically characterize cancer on a granular level. Although Next Generation Sequencing (NGS) is becoming part of the common practice, little is known on the role of a characterization on a gene variant level. Large heterochromatic regions or blocks are a characteristic feature in the autosomes 1, 9, 16 and the blocks contain about 10% of the human genome. The heterochromatic regions consist of highly repetitive DNA of the classes Sat I to IV. Thus, these specific regions are preferential positions for genome instability. The aim of this study was to explore the feasibility of a gene variant-oriented characterization for variants interplay discovery and to explore the role of chromosome stability in gene variants incidence. Methods: This study analyzed a pilot cohort of 35 metastatic breast cancer (MBC) patients (pts) treated and characterized for CTCs and circulating tumor DNA (ctDNA) at Northwestern University (Chicago, IL). ctDNA was analyzed using the PredicinePLUS™ NGS 180-gene panel (Predicine Inc, CA). Associations between gene variants and clinico-molecular characteristics were tested through Fisher’s exact test. Chromosomes 1, 9, 16 where defined as instable (instable_chr) based on the presence of highly repeated sequences. Results: An overall set of 35 samples was analyzed, and the main variants were detected in the ARID1A (40%), ATM (20%), DNMT3A (37%), ESR1 (20%), PIK3CA (26%), and TP53 (49%) genes. A total of 448 gene variants were detected through the NGS panel and across them, ARID1A accounted for 5.13%, ATM 2.23%, DNMT3A 4.91%, ESR1 4.02%, PIK3CA 2.23%, and TP53 for 6.03%. Among the genes mutated, the DNMT3A:c.2644C&gt;T, DNMT3A:c.2645G&gt;A, ESR1:c.1138G&gt;C,ESR1:c.1609T&gt;A, ESR1:c.1610A&gt;C, ESR1:c.1613A&gt;G, PIK3CA:c.1624G&gt;A were the most detected. Thirty-eight copy number variations (CNV) and 3 splicing variants were observed. Notably, 55.6% of detected variants were found in instable_chr. No significant differences were observed between instable_chr variants and MBC subtype. Interestingly, ARID1Aaberrations were significantly linked to ATM, ESR1 (P=0.006) and PIK3CA with ESR1 (P= 0.019). Consistently with literature, ATM and TP53 variants were mutually exclusive (P&lt;0.0001). Intriguingly, both ATM and TP53 were associated with a higher incidence of variants affecting genes in instable_chr. Conclusions: MBC is often described as a non-gene-addicted disease, rendering the onset of gene variants a multi-factor phenomenon. The present results suggest a role for both chromosomal intrinsic instability and DNA repair impairment in this process, with a potential down-stream selection mediated by treatment resistance. Future studies are warranted to further validate this proof of concept approach.

Citation Format: Lorenzo Gerratana, Qiang Zhang, Ami N Shah, Alessandra Franzoni, Jianjun Yu, Shidong Jia, Andrew A Davis, Youbin Zhang, Firas Wehbe, Amir Behdad, Leonidas C Platanias, William J Gradishar, Massimo Cristofanilli. Next generation sequencing-based gene variant-oriented characterization in metastatic breast cancer: An innovative analysis using ctDNA [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 P5-01-10.