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

PURPOSE

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

PATIENTS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Searching for the "Holy Grail" of breast cancer recurrence risk: a narrative review of the hunt for a better biomarker and the promise of circulating tumor DNA (ctDNA)

BACKGROUND

This paper is a narrative review of a major clinical challenge at the heart of breast cancer care: determining which patients are at risk of recurrence, which require systemic therapy, and which remain at risk in the survivorship phase of care despite initial therapy.

METHODS

We review the literature on prognostic and predictive biomarkers in breast cancer with a focus on detection of minimal residual disease.

RESULTS

While we have many tools to estimate and refine risk that are used to individualize local and systemic therapy, we know that we continue to over treat many patients and undertreat others. Many patients also experience what is, at least in hindsight, needless fear of recurrence. In this review, we frame this dilemma for the practicing breast oncologist and discuss the search for what we term the "holy grail" of breast cancer evaluation: the ideal biomarker of residual distant disease. We review the history of attempts to address this problem and the up-to-date science on biomarkers, circulating tumor cells and circulating tumor DNA (ctDNA).

CONCLUSION

This review suggests that the emerging promise of ctDNA may help resolve a crticical dilemma at the heart of breast cancer care, and improve prognostication, treatment selection, and outcomes for patients with breast cancer.

Managing hyperglycemia and rash associated with alpelisib: expert consensus recommendations using the Delphi technique

Hyperglycemia and rash are expected but challenging adverse events of phosphatidylinositol-3-kinase inhibition (such as with alpelisib). Two modified Delphi panels were conducted to provide consensus recommendations for managing hyperglycemia and rash in patients taking alpelisib. Experts rated the appropriateness of interventions on a 1-to-9 scale; median scores and dispersion were used to classify the levels of agreement. Per the hyperglycemia panel, it is appropriate to start alpelisib in patients with HbA1c 6.5% (diabetes) to <8%, or at highest risk for developing hyperglycemia, if they have a pre-treatment endocrinology consult. Recommend prophylactic metformin in patients with baseline HbA1c 5.7% to 6.4%. Metformin is the preferred first-line anti-hyperglycemic agent. Per the rash panel, initiate prophylactic nonsedating H1 antihistamines in patients starting alpelisib. Nonsedating H1 antihistamines and topical steroids are the preferred initial management for rash. In addition to clinical trial evidence, these recommendations will help address gaps encountered in clinical practice.

Abstract 4353: Utilizing scRNA sequencing to understand biomarkers of response and resistance to Sacitizumab Govetican in localized TNBC

Triple-Negative Breast Cancer (TNBC) is an aggressive breast cancer subset, which lacks expression of estrogen receptors, progesterone receptors, and human epidermal growth factor receptor-2. This subset of breast cancer disproportionately affects Black and African American women and improving TNBC treatment options is vital to reducing breast cancer mortality. The novel antibody-drug conjugate, Sacitizumab Govetican (SG), which targets TROP2 at the cell surface, has shown promising clinical results from the NeoSTAR trial (NCT04230109), a phase II study evaluating neoadjuvant SG therapy in a localized TNBC setting. As part of the NeoSTAR clinical trial, we have collected and processed pre- and post- SG treatment patient samples, with the aim of understanding response to this monotherapy. Herein, we identify biomarkers of response and resistance to SG monotherapy through the use of single cell RNA sequencing of matched pre- and post-treatment patient biopsies combined with exome sequencing these patient samples. Pre-treatment core needle biopsy samples, and if applicable, post-treatment residual disease biopsies were dissociated into single cell suspensions and subjected to single cell RNA sequencing. Additionally, fixed patient tissue samples were processed accordingly for exome sequencing analyses. Overall, we analyzed over 144,000 cells from 37 total scRNA seq libraries with an average of 3800 cells per biopsy sample, demonstrating the feasibility of this method. From these analyses, we observed several cell-type differences between patients who achieved a pathological complete response (pCR) and patients who had residual disease (RD). Specifically, our data shows that tumor infiltrating lymphocytes are a potential prognostic biomarker of response to SG. Furthermore, we detected alterations in among stromal and immune cell subsets, among non-responders, indicating that these cell types maybe indicative of SG resistance. Taken together, we outline biomarkers of response to SG treatment for an improved understanding of resistance mechanisms in the neoadjuvant setting to improve TNBC outcomes among patients.

Citation Format: Nicole Peiris, Simona Cristea, Mengran Zhang, Siang Koh, James Coates, Ilze Smidt, Veerle Bossuyt, Laura Spring, Aditya Bardia, Leif Ellisen. Utilizing scRNA sequencing to understand biomarkers of response and resistance to Sacitizumab Govetican in localized TNBC. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4353.

Metaplastic breast cancer: A review

Metaplastic breast cancer (MpBC) is an uncommon aggressive malignancy that is associated with a poor prognosis. Due to its rarity, the relationships between the clinical and pathological features of MpBC, treatment approach, and clinical outcomes remain underexplored. In the following review article, we synthesize the existing data on the clinical, pathological and genomic features, management, and outcomes of MpBC. We also identify potential targets for future clinical trials.

Antibody-Drug Conjugates in Breast Cancer: Spotlight on HER2

ABSTRACT

Antibody-drug conjugates (ADCs) are composed of monoclonal antibodies linked to a cytotoxic payload, enabling targeted delivery of more potent chemotherapy. In the past decade, there has been rapid development of ADCs aimed at different types of breast cancer. The success of the monoclonal antibody trastuzumab has led to the evolution of several ADCs targeting HER2-positive breast cancer. Trastuzumab-emtansine, the first approved ADC targeting HER2-positive breast cancer, has become standard of care for patients with high-risk early-stage HER2-positive breast cancer who have residual disease after neoadjuvant chemotherapy. More recently, the observation of the bystander effect, in which ADCs target both antigen-positive cells and adjacent antigen-negative cells, has led to the reclassification of "HER2-low" breast cancer and the development of trastuzumab-deruxtecan to target this population. This article reviews the history of HER2-directed ADCs in breast cancer as well as ongoing ADCs in development.

Expert consensus recommendations for managing hyperglycemia and rash in patients with PIK3CA-mutated, hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2–) advanced breast cancer (ABC) treated with alpelisib (ALP)

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Background: ALP is a PI3Kα inhibitor and degrader approved with fulvestrant for the treatment (tx) of patients (pts) with PIK3CA-mutated, HR+, HER2– ABC. Hyperglycemia (HG) and rash are expected adverse events with ALP tx and remain a challenge for physicians and pts. Management guidance is primarily based on clinical trial experience, which is not necessarily reflective of real-world pts. Here we report guidance for optimizing prevention and management of HG and rash in pts taking ALP based on an integrated Delphi panel, a systematic, validated approach to organize consensus from experts in the absence of definitive evidence. Methods: Two modified Delphi panels were conducted, focusing on HG and rash, respectively. Each panel included 4 oncologists, 4 endocrinologists or dermatologists, 1 clinical pharmacist, and 1 pt advocate. Experts were asked to rate appropriateness of 908 interventions for HG and 348 for rash on hypothetical pt scenarios on a 1 (highly inappropriate) to 9 (highly appropriate) scale. Results were reviewed at virtual meetings, after which experts repeated the rating. The level of agreement or disagreement was determined using the median scores and dispersion from the final rating, and this level of agreement was used to develop consensus statements and tx algorithms. Results: Per the HG panel, (a) ALP tx is appropriate in individuals with HbA1c 6.5% to < 8% with a pre-tx endocrinology consult; (b) low carbohydrate diet is appropriate in all pts starting ALP; (c) prophylactic metformin is appropriate in pts with baseline HbA1c 5.7%-6.4%; may also be appropriate in pts with HbA1c < 5.7%; (d) after metformin, an SGLT2 inhibitor or a thiazolidinedione is an appropriate second-/third-line anti-HG agent (or first-line in metformin-intolerant pts), while insulin is not. Per the rash panel, (a) prophylactic nonsedating (NS) H1 antihistamines (standard dose) are appropriate for all pts; (b) starting/escalating NS H1 antihistamines and topical steroids (TS) is the preferred first step for managing rash; (c) it is appropriate to add, but not replace with, a sedating H1 antihistamine, if response to high-dose, NS option is inadequate, and to add an H2 antihistamine if response is still inadequate; (d) it is appropriate to hold ALP and start oral corticosteroids (OCS) if rash affects > 30% body surface area and is recurrent or has moderate/severe symptoms; (e) if angioedema is present, it is appropriate to either hold ALP and start OCS, or permanently discontinue ALP tx. Conclusions: Until further evidence is available, these expert recommendations provide guidance on prevention and management of HG and rash related to ALP tx in routine clinical practice.

Discordance in management of adverse events associated with oral therapies in hormone receptor–positive breast cancer among health care providers and experts: Findings from an online decision support tool

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Background: Oral targeted therapies (OTTs) inhibiting CDK4/6, PI3K, and mTOR have established roles across multiple lines of therapy in patients with advanced hormone receptor–positive, HER2-negative breast cancer (HR+ BC). Abemaciclib, a CDK4/6 inhibitor (i), now also is approved in the adjuvant setting for eligible patients with early-stage HR+ BC. These OTTs are associated with various adverse events (AEs), such as cytopenias, diarrhea, hepatotoxicity, and rash. Optimal AE management is critical to promote patient adherence and achieve the best possible outcomes. Here we report an analysis of healthcare professional (HCP) management of AEs associated with OTTs in HR+ BC using an online decision support tool. Methods: The online tool was developed with 5 BC experts providing recommendations on the management of AEs associated with OTTs. Within the online tool, HCPs were prompted to input relevant patient case details through a series of predefined questions, including which OTT and type of AE the patient is experiencing, along with their management approach. Participants were then shown an expert recommendation based on the specific characteristics of that case and were asked if their management plan changed based on that recommendation. Results: Between September 2021 and April 2022, 557 cases were entered by 390 participants. Among 291 cases of patients currently receiving oral therapy, CDK4/6i therapy was most commonly selected (82%), followed by PI3Ki (11%) and mTORi (8%) therapy. The most common AE reported for CDK4/6i, PI3Ki, and mTORi therapy were cytopenias (56%), hyperglycemia (64%), and stomatitis (57%), respectively. With CDK4/6i, HCPs were discordant with expert recommendations for management of AEs reported in 44%, 39%, and 35% of entered cases with ribociclib, abemaciclib, and palbociclib, respectively. The greatest variance between HCP and expert recommendations were with management of VTE, hepatotoxicity, QT prolongation, and rash (Table). Among HCPs with discordant results from the experts, 50% changed their AE management plan after viewing the expert recommendation. Conclusions: These data suggest that HCPs may be challenged to optimally manage AEs related to OTTs in patients with HR+ BC. Use of an online tool may enhance HCP management of these AEs for patients with HR+ BC. A detailed analysis of the tool, including HCP planned management vs expert recommendations, will be presented.[Table: see text]

Abstract 2638: Sacituzumab Govitecan, combination with PARP inhibitor, Talazoparib, in metastatic triple-negative breast cancer (TNBC): Translational investigation

Background: Sacituzumab Govitecan (SG), the first antibody-drug conjugate approved for metastatic TNBC (mTNBC), is comprised of SN-38 (active metabolite of irinotecan), a topoisomerase I (TOP1) inhibitor, coupled via a hydrolyzable linker to monoclonal antibody targeting trophoblast cell surface antigen 2 (Trop-2), an antigen overexpressed in mTNBC. Poly (ADP-ribose) polymerase inhibitors (PARPi) block resolution of TOP1 cleavage complexes (TOP1CCs) induced by TOP1 inhibitors, thus unmasking the inability of remaining pathways to repair DNA damage. However, previous clinical trials combining PARPi with standard TOP1 inhibitors (irinotecan, topotecan) were terminated early due to dose-limiting myelosuppression. We evaluated the combination of SG with PARP inhibitor in both pre-clinical models and phase 1b clinical trial.

Methods and Results: In pre-clinical models we demonstrated that the targeted antibody-based delivery of SN-38 increased the ratio of tumor-to-normal cell SN-38, resulting in stabilized TOP1CCs, enhanced DNA damage and increased cytotoxicity with the combination, selectively in tumor cells but not normal cells, despite temporal separation of SG and PARPi exposure. To validate the hypothesis, we conducted a phase 1b investigator-initiated clinical trial combining SG with PARPi (talazoparib) in patients with mTNBC (NCT04039230). Inclusion criteria included female patients ≥ 18 years of age with mTNBC (per ASCO/CAP guidelines) and previous treatment with at least one prior therapeutic regimen for mTNBC. Clinical outcomes were assessed by Objective Response Rate per RECIST v1.1. In the phase 1b clinical trial (SG day 18, every 21 days with talazoparib), the staggered schedule with supportive therapy was relatively well-tolerated without DLTs, as predicted by the pre-clinical models. Furthermore, the staggered schedule demonstrated promising clinical activity. Molecular analysis of paired pre-treatment and on-treatment specimens demonstrated γ-H2AX accumulation, confirming pharmacodynamic inhibition with combination therapy. The dose-escalation portion of clinical trial successfully completed enrollment with a recommended phase-2 dose (R2PD) of sequential SG (10 mg/kg on days 1,8) with talazoparib (1 mg on days 15-21), every 21 days.

Conclusion: Staggered dosing of SG and PARPi, leveraging the selective drug delivery mechanism of SG to minimize toxicity while maintaining efficacy, was feasible and demonstrated encouraging evidence of clinical activity with objective responses among patients with mTNBC. The translational study highlights how mechanistic insights and innovative scheduling could be utilized to develop promising drug combinations, including previously rejected combinations, for patients with mTNBC.

Citation Format: Aditya Bardia, James T. Coates, Laura Spring, Sheng Sun, Dejan Juric, Nayana Thimmiah, Andrzej Niemierko, Phoebe Ryan, Ann Partridge, Jeffrey Peppercorn, Heather Parsons, Seth Wander, Kelsey Pierce, Victoria Attaya, Donna Fitzgerald, Brenda Lormil, Maria Shellock, Aiko Nagayama, Veerle Bossuyt, Bev Moy, Sara Tolaney, Leif Ellisen. Sacituzumab Govitecan, combination with PARP inhibitor, Talazoparib, in metastatic triple-negative breast cancer (TNBC): Translational investigation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2638.

Survival of elderly patients with HER2+/HR- metastatic breast cancer in clinical practice: SEER-Medicare data 2012-2016

1039

Background: Older patients with human epidermal growth factor 2-positive (HER2+) metastatic breast cancer(mBC) are underrepresented in clinical trials. We aim to assess the overall survival (OS) and breast cancer-specific survival of elderly women with de novo HER2+/hormone receptor-negative (HR-) mBC in a real-world setting. Methods: Elderly women with HER2+/HR- mBC treated with chemotherapy and/or HER2-targeted agents and with continuous Medicare Part A, B, and D coverage 1-year before diagnosis were identified from the SEER-MEDICARE database 2012-2016. Patients were retrospectively followed from metastatic diagnosis until death, disenrollment from Medicare A, B, or D, or end of the observation period. Patients' year and month of diagnosis and death were retrieved from SEER. Death dates were verified with Medicare records reported by the Social Security Administration (SSA). For all-cause deaths, Kaplan-Meier analysis was used to estimate overall survival. The cumulative incidence competing risk (CICR) method based on cumulative incidence function (CIF) was used to estimate breast cancer-specific death incidence. Results: Seventy-three patients (mean age at diagnosis, 75.0±7.7 years) met the inclusion criteria. Among them, 56 were treated with trastuzumab ± pertuzumab /chemotherapy as first-line treatment, and 17 were treated with chemotherapy only. The median time to initiate trastuzumab-based treatment from diagnosis was 2.5 months, and the longest trastuzumab treatment length was over 44 months. The median follow-up for OS was 13 months. One patient developed stomach cancer 6 months after breast cancer diagnosis. In Kaplan-Meier analysis, censoring or not censoring this patient after second cancer development resulted in a median OS of 19 months (95% CI, 9-24 months) and 18 months (95% CI, 9-22 months). The OS at the end of 46 months was approximately 25%. Five patients died from other causes, including lung cancer, cerebrovascular diseases, aortic aneurysm and dissection, pneumonia and influenza, and heart diseases during treatment. Considering these competing risks, 50% (95% CI, 36%-64%) of patients specifically died from breast cancer between 21 and 22 months, estimated by the CICR method. Conclusions: Our study observed a shorter OS among HER2+/HR- mBC elderly patients in clinical practice than the OS of 40.8 and 56.5 months among younger patients in the CLEOPATRA trial, suggesting that age is an important prognostic factor for breast cancer survival. The presence of second cancer and other competing risks led to overestimating the probabilities of breast cancer-specific death and resulted in a shorter OS using the Kaplan-Meier method. The CICR method is more relevant to estimate the breast-cancer-specific death incidence.

Baseline preferences for digital information engagement in patients with breast cancer by age and status of diagnosis

e24119

Background: The need for improvement in education and decision-making support for patients with breast cancer is well documented. Digital health applications offer potential to address these needs through widely available smartphone technology. Understanding patients’ baseline preferences for information sources, breast cancer-related topics of interest, and current use of smartphones and how these interests may differ based on demographic and clinical factors can inform the development of a patient-centered digital navigation tool. Methods: As part of a pilot trial of the Outcomes4Me breast cancer navigation app, we conducted a baseline cross-sectional survey of patients presenting for routine breast cancer care at an academic medical center and community-based sites. Eligible patients had invasive breast cancer of any stage and were actively in treatment. Survey-specific questions addressed sources of cancer information and informational needs. Analysis is descriptive with statistical comparisons based on Fisher’s exact test. Results: Ninety out of 107 patients in the pilot trial completed the survey items of interest. The majority of patients were over age 50 (59%) and 35% had stage IV disease. Baseline reported uses for mobile devices included text (67%), email (61%), phone (47%), social media (41%), accessing the internet (18%), and apps (12%). Only 7% of patients noted using mobile apps for navigating disease and treatment options. When asked to rank the importance of cancer information sources, 88% and 42% of patients reported relying heavily on their oncologist and the rest of the care team, respectively. Forty percent of patients relied at least moderately on the internet for health information and 27% on online support groups, with patients < age 50 more likely than those > age 50 to rely on online support groups for health information (41% vs 17%, P = 0.02). The most common educational needs reported were side effects (79%), followed by prognosis (72%), healthy lifestyle (71%), treatment options (70%), general breast cancer news and research (67%), information about their current cancer status (59%), potential clinical trials (44%), and costs of treatment (14%). Patients with metastatic breast expressed greater interest in information about clinical trials compared to those without metastatic disease (64% vs 36%, P = 0.01), and less interest in information about prognosis (54% vs. 81%, P = 0.01). Conclusions: Despite reliance on their oncologist and oncology team for information, patients report multiple unmet educational needs related to their disease and treatment options. While a substantial percentage of patients with breast cancer turn to the internet for information, there is untapped potential to use mobile devices to improve patient education and awareness of treatment options, including clinical trials.

Adjuvant trastuzumab and vinorelbine (TV) for early-stage HER2+ breast cancer

e12521

Background: The anti-HER2 antibody trastuzumab has vastly improved outcomes for women with early stage and advanced HER2+ breast cancer (BC) when used in combination with chemotherapy. Anthracycline and taxane-based regimens have historically made up the chemotherapy backbone for patients with localized HER2+ BC, though recent evidence suggests anthracyclines can be safely omitted. The single arm phase II APT trial established trastuzumab and paclitaxel as the standard adjuvant regimen for small HER2+ tumors. However, paclitaxel requires weekly treatment, causes alopecia, and has high rates of neuropathy and hypersensitivity reactions. In patients with metastatic HER2+ BC, the combination of trastuzumab and vinorelbine (TV) is effective and well tolerated. There is a need for alternative regimens for patients with HER2+ early-stage BC, especially for those with contraindications to anthracycline and taxane-based regimens. We conducted a retrospective study of patients with early stage HER2+ BC treated with adjuvant TV to evaluate a non-anthracycline/taxane-based, alopecia-sparing regimen. Methods: Clinicopathological characteristics, treatment details, and outcomes of patients with localized HER2+ BC treated with adjuvant TV for from 2007 to 2021 at a large academic medical institution were collected. Study endpoints included invasive disease-free survival (IDFS), overall survival (OS), and safety/tolerability. IDFS and OS were measured from start date of TV treatment to date of event or last follow-up, respectively. 5-year survival rates were generated in GraphPad Prism. Results: A total of 25 patients were treated with TV. All patients received trastuzumab at standard dosing and vinorelbine at a starting dose of 25 mg/m2 on days 1/8 of a 21-day cycle with 4 planned cycles. Median age at diagnosis was 61 years (range: 36-81). 88% of patients had anatomic pathologic Stage IA BC and 12% Stage IIA BC. Of the 25 patients, 24 of them opted to pursue TV due to concerns over alopecia, neuropathy, and other toxicities while 1 patient had received prior adriamycin and therefore opted for TV. With a median follow-up time of 68 months (5.7 years), the 5-year rate of survival from invasive disease was 90.9%, with 1 local and 1 distant recurrence. The 5-year overall survival was 100%. 76% of patients completed 4 cycles of TV without dose holds or delays and 92% completed 4 cycles without dose reductions. 2 patients required hospitalization during treatment with TV due to toxicity (diarrhea attributed to V, rigors/fever attributed to T). No patients experienced alopecia or long-term neuropathy. Conclusions: Trastuzumab in combination with vinorelbine in the adjuvant, early-stage setting for HER2+ BC is effective and well-tolerated and warrants further exploration as an alternative to taxane-based regimen.

TRIO-US B-12 TALENT: Phase II neoadjuvant trial evaluating trastuzumab deruxtecan with or without anastrozole for HER2-low, HR+ early-stage breast cancer

TPS623

Background: Although patients with hormone receptor-positive (HR+)/HER2-negative breast cancer (BC) frequently experience disease response to neoadjuvant therapy, fewer than 10% achieve a pathologic complete response (pCR) with standard chemotherapy or endocrine therapy, even in combination with CDK4/6 inhibitors. Thus, finding more effective therapies for this disease remains an area of unmet need. HER2 amplification is a known driver of endocrine resistance and HER2 may be expressed at a low level (IHC 1+ or 2+) in approximately 60% of HR+ BC. Trastuzumab deruxtecan (DS-8201a, T-DXd) is a novel HER2-targeting antibody drug conjugate (ADC) that is FDA approved in the US for HER2-positive (with boxed warnings for interstitial lung disease) and has demonstrated promising clinical efficacy in HER2-low BC with an objective response rate of ̃37%. The aim of TALENT (TRIO-US B-12, NCT04553770) is to evaluate the clinical activity and safety of neoadjuvant T-DXd alone or in combination with endocrine therapy in patients with HR+/HER2-low early BC. Methods: This is an ongoing randomized, multicenter, open-label, two-stage, phase II neoadjuvant trial for participants with early stage, HR+, HER2-low (1+ or 2+/ISH- by IHC) BC. Eligible participants include men and women with previously untreated, operable invasive BC greater than 2.0 cm (cT2). Pts with recurrent, metastatic, or inflammatory BC are excluded. Pts are randomized 1:1 to receive six to eight cycles of T-DXd (5.4 mg/kg IV q21 days) alone or in combination with anastrozole AI (1 mg PO QD). Men and pre/peri menopausal women randomized to the AI arm also receive routine care GnRH agonist. Stratification factors include HER2 expression and menopausal status (men stratified as postmenopausal). Tumor tissue is taken at baseline, cycle 1 day 17-21, and at surgery. Blood samples are taken at 4 time points for biomarker analysis. The primary endpoint is pCR rate (breast and lymph node) at definitive surgery. In stage I, 58 participants will be randomized (29/arm). If >2 participants in an arm achieve pCR, that arm will expand (stage II) to enroll an additional 15 participants (total of 44/arm). A pCR rate of > 10% (5/44) would be considered favorable, warranting further evaluation in a larger trial. Other endpoints include safety, changes in Ki67 expression, Residual Cancer Burden index, biomarker analysis (including serial cfDNA analysis), and health-related quality of life. As of January 2022, 37 participants have enrolled, 24 have completed treatment, and 14 have had surgery. To our knowledge this is the first and only ongoing study evaluating T-DXd with or without endocrine therapy for HR+, HER2-low BC in the neoadjuvant setting. The study will shed light on clinical activity and biomarkers, which may guide larger confirmatory studies for this population. Clinical trial information: NCT04553770.

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

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

Impact of ribociclib (RIB) dose modifications (mod) on overall survival (OS) in patients (pts) with HR+/HER2- advanced breast cancer (ABC) in MONALEESA(ML)-2

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Background: The phase 3 ML-2, -3, and -7 trials all demonstrated consistent and statistically significant OS benefit with RIB (starting dose: 600 mg/d 3 wk on/1 wk off) vs PBO in pts with HR+/HER2− ABC. RIB dose mod (reductions and/or interruptions) when needed did not impact OS benefit with RIB + endocrine therapy (ET) in previous analyses of ML-3/-7. Here we present data on the effect of RIB dose mod on OS in postmenopausal pts with HR+/HER2− ABC in ML-2. Methods: ML-2 (NCT01958021) enrolled postmenopausal pts randomized 1:1 to first-line RIB + letrozole (LET) or PBO + LET. Landmark (LM) analyses of OS were performed to evaluate the association between dose reductions (yes vs no) and OS. Multiple LM times were considered to determine the sensitivity of the findings. As an alternative to LM analysis, a Cox proportional hazards model with a time-varying covariate was performed. Two time-dependent variables, dose reduction (with/without mod from 600 mg starting dose) and relative dose intensity 2 (RDI2), were included in the respective model as covariates to explore the association with OS. To account for differences in time to first dose mod, RDI2 reflects the post–dose mod period. Median (m) OS was obtained using a modified Kaplan-Meier method. Results: At data cutoff (June 10, 2021; m follow-up, 49.35 [range, 0-86.7] mo), 209 of 334 pts (62.6%) had ≥ 1 RIB dose reduction and 125 of 334 (37.4%) had 0 RIB dose reduction. LM analyses by dose reduction are presented (Table). mOS was 66.0 (95% CI, 57.6-75.7) mo in pts with ≥ 1 RIB dose reduction vs 60.6 (95% CI, 42.5-79.2) mo in pts with no RIB dose reductions (HR, 0.87 [95% CI, 0.65-1.18]). RDI2 was classified according to tertile: low (< 64.27%), medium (64.27%-95.86%), and high (> 95.86%). In pts with low, medium, and high RDI2, mOS was 62.6 (95% CI, 50.0-80.7) mo, 63.9 (95% CI, 48.8-not reached [NR]) mo, and 65.3 (95% CI, 50.5-NR) mo, respectively (HR low vs high, 0.99 [95% CI, 0.69-1.42]; HR medium vs high, 0.97 [95% CI, 0.62-1.38]). Conclusions: In this exploratory analysis of ML-2, OS benefit was maintained in pts with HR+/HER2− ABC who required mod from the recommended starting dose of RIB (600 mg/d 3 wk on/1 wk off). No relationship was observed between OS and RIB dose reduction or RDI2; OS benefit with RIB was observed in all groups. Clinical trial information: NCT01958021. [Table: see text]

Neoadjuvant HER2-targeted therapy +/- immunotherapy with pembrolizumab (neoHIP): An open-label randomized phase II trial

TPS624

Background: Immune checkpoint inhibition (ICI) is synergistic with HER2-directed therapy in pre-clinical models. Clinically, pembrolizumab (K)-mediated ICI plus HER2-directed therapy with trastuzumab (H) was safe and demonstrated modest activity in H-resistant HER2-positive (HER2+) metastatic breast cancer. Because ICI may confer more robust activity when administered earlier in the course of disease, H and K administered in the curative-intent, treatment-naive setting may allow for de-escalation of cytotoxics; confer life-long, tumor-specific immunity; and ultimately, improve cure rates. Moreover, the synergy of H and K with paclitaxel (T) may overcome the need for dual HER2-blockade with H plus pertuzumab (P). In this randomized, multicenter, phase II, open-label trial the efficacy and safety of neoadjuvant THP vs THP-K vs TH-K are explored. Methods: 174 patients (pts) ≥18y with previously untreated, stage II-III, HER2+ breast cancer will be randomized and stratified by clinical nodal status (positive vs. negative) and hormone receptor status (positive vs. negative). In arm A, pts receive T at 80mg/m2 weekly for 12 weeks, H at 8mg/Kg (loading dose) and then 6mg/Kg every 3 weeks x 3 doses, P at 840 mg (loading dose) and then 420mg/Kg every 3 weeks x 3 doses (THP). In arm B, pts receive THP plus K at 200mg every 3 weeks x 4 doses (THP-K). In arm C, pts receive TH-K. Definitive surgery is 3-6 weeks after the last dose. After surgery, pts are treated per the treating physician’s discretion including radiotherapy per local clinical standard. Pts whose tumors are hormone-receptor positive will receive hormone therapy per local standard-of-care. The primary end point is pathologic complete response (pCR) rate in the breast and axilla (ypT0/Tis ypN0). Secondary end points include pCR rate by ypT0ypN0 and ypT0/Tis, residual cancer burden index, event free survival, breast conserving surgery rate, safety and overall survival. Exploratory correlative studies will characterize potential immune biomarkers predictive of efficacy and/or toxicity. Clinical trial information: NCT03747120.

Pilot study to assess prolonged overnight fasting in breast cancer survivors (longfast)

PURPOSE

Retrospective analysis of nightly fasting among women with breast cancer suggests that fasting < 13 h may be associated with a higher risk of breast cancer recurrence. We sought to evaluate prolonged overnight fasting (POF), an accessible nonpharmacological intervention, in a prospective feasibility study.

METHODS

We designed a single-arm, pilot study to evaluate the feasibility of fasting for 13 h overnight for 12 weeks among women with a history of early-stage breast cancer survivors. Baseline and end of study assessments included measurements of body mass index (BMI), blood biomarkers, quality of life (QOL), mood, fatigue, and physical activity. Patient-reported outcome questionnaires were also administered at 6 weeks. Feasibility was defined as ≥ 60% of participants documenting fasting for 13 h on at least 70% of nights during the study period.

RESULTS

Forty women with a history of breast cancer were enrolled with a median age of 60 (range 35-76) and median time since diagnosis of 4.5 years (range 0.8-20.7). At baseline, BMI was ≥ 25 in 37.5%. Ninety-five percent of participants fasted ≥ 13 h for at least 70% of study days (95% CI 83-99%). There was a statistically significant improvement in anxiety (p = 0.0007) at 6 weeks and BMI (p = 0.0072), anxiety (p = 0.0141), depression (p = 0.0048), and fatigue (p = 0.0105) at 12 weeks. There was no significant change in overall QOL, physical activity levels, or blood biomarkers at 12 weeks.

CONCLUSIONS

POF is feasible among patients with a history of breast cancer and may potentially improve BMI, mood, and fatigue without detrimental effects on overall QOL.

Abstract P2-14-17: A phase 1b study of PVX-410 vaccine in combination with pembrolizumab in metastatic triple negative breast cancer (mTNBC)

Background: Immunotherapy with checkpoint inhibition is active in mTNBC. Both pembrolizumab and atezolizumab are FDA approved for programmed cell death ligand 1 positive (PDL1+) mTNBC. Vaccines may further induce host immune response and enhance therapeutic activity of checkpoint inhibitors. PVX-410 (PVX) (OncoPep, Inc.) is a novel, HLA-A2 restricted, tetra-peptide vaccine, with 3 of its 4 antigens (XBP1[2 splice variants] and CD138) commonly overexpressed in TNBC. We present results from a phase 1b study evaluating the immune response, safety and tolerability, and clinical activity of PVX and pembrolizumab (PEM) in mTNBC. Methods: Eligibility for this phase 1b multi-center, single-arm study included HLA-A2+, PD-L1 unselected female patients (pts) ≥18 years with metastatic or inoperable locally advanced TNBC, measurable disease, and any number of prior therapies, including prior checkpoint inhibitor therapy. Pts received 6 doses of 800µg PVX emulsified in Montanide ISA 720 VG by subcutaneous injection co-administered with intramuscular Hiltonol weekly for 6 weeks (wks) followed by booster vaccine doses at wks 10 and 28, with concurrent intravenous 200 mg PEM every 3 wks starting with the second PVX dose. Therapy was given until progressive disease, unacceptable toxicity or a maximum of 24 months. Blood samples were scheduled for immune response assessment at baseline and at weeks 2, 5, 10, 28, and 52 post-treatment initiation. The primary objective was PVX- specific immune response at week 10. Immune response was defined as a ≥2-fold change over baseline in the proportion of CD3+CD8+ T cells that expressed IFNγ and the proportion of CD3+CD8+ T cells positive for PVX tetramers following an in vitro stimulation of PBMC with PVX peptides using a flow cytometric assay. Secondary objectives were immune response at wk 28, safety and tolerability, and clinical endpoints (RR, CBR, DCR, DoR, PFS, and OS). Results: Between 3/2018 and 8/2020, 19 pts enrolled. Median age was 62 yrs (range 46-79), with median 2 (range 0-9) lines of prior therapy for metastatic disease. Median disease-free interval among 16 pts with prior early TNBC was 3.3 years. Among 19 enrolled patients, 16 were available for analysis at the time of abstract submission. Among the 16, 10 pts were evaluable at week 10 and 7(70%) demonstrated a PVX specific immune response. There were 6 patients who progressed before week 10, of whom 3 (50%) had a positive immune response at the EOT visit. Immune response persisted in all evaluable pts assessed at week 28 (n=4). Immune response data for all evaluable patients will be updated at the presentation. Among 19 patients evaluable for safety analysis, the most common adverse events (AEs) attributable to PVX (grade ≥2) included: fatigue (21%), arthralgia (11%) injection site reaction (5 %) pain (5%) lymphocyte count decreased (5%), maculopapular rash (5%) and skin infection (5%) . There were two grade 3 AEs attributed to PEM (AST elevation, hyponatremia) and one grade 4 AE (ALT elevation). There were no grade 5 AEs. The clinical benefit rate (CR+PR+SD for ≥16 weeks) was 31.6% with no confirmed partial or complete responses. Best overall response was SD in 9 (47%) patients. Analysis of additional clinical endpoints including PFS and OS is ongoing and will be presented at the meeting. Conclusions: PVX plus PEM is safe with manageable toxicity in pts with mTNBC. No new unexpected adverse events were identified. Immune response data show PVX induces antigen-specific T cell expansion as observed by increases in PVX tetramer and IFN positive T cells. Clinical disease control was observed with a CBR of 31.6%. Based on these promising immune response results in this pretreated population, a phase 2 study with PVX+PEM in combination with standard chemotherapy in treatment naïve, PD-L1+ mTNBC is underway (NCT04634747).

Citation Format: Steven J Isakoff, Nadine M. Tung, Jun Yin, Nabihah Tayob, Joanne Parker, Julie Rosenberg, Aditya Bardia, Laura Spring, Hannah Park, Maya Collins, William T. Barry, Mariano Severgnini, Doris Peterkin, Sara M. Tolaney. A phase 1b study of PVX-410 vaccine in combination with pembrolizumab in metastatic triple negative breast cancer (mTNBC) [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 P2-14-17.

Abstract P4-12-08: Accuracy of Patient Self-Reported Breast Cancer Disease Characteristics Compared to the Medical Record in a Trial of the Outcomes4MeDigital Health App

Background: Patients’ understanding of their breast cancer (BC) diagnosis is important in improving treatment adherence, shared decision-making, and clinical trial matching. However, studies have reported discrepancies between electronic medical record (EMR) and patient reported information. Using data collected from a pilot study of the Outcomes4Me patient empowerment and clinical trial matching App, we analyzed concordance of patient reported disease characteristics compared to EMR data. Methods: Data was analyzed from a single institution pilot study (NCT04262518) evaluating the feasibility of introducing the Outcomes4Me app into routine BC care. Eligibility included BC patients with any subtype or stage of invasive cancer presenting with a new diagnosis or for follow-up on active therapy. We compared patient reported characteristics within a study specific survey and/or the Outcomes4Me app for stage (metastatic or not metastatic), recurrence history, hormone receptor status, HER2, and surgery history with the data recorded in the EMR. All statistics were descriptive. We conducted the same comparison between patient reported clinical characteristics among real world users of the Outcome4Me app and EMR records downloaded by that cohort of patients. Results: Between June 2020 and December 2020, 107 patients were enrolled. Baseline demographics: 90% White, 4% Black, 3% Asian; 37% with a college degree, and 43% with post college education; 66% hormone positive/HER2-, 20% HER2+, and 13% triple negative BC; 31% were stage 4. Concordance between the survey or App questionnaire and the EMR is shown in the Table. Comparing EMR and survey data, 62% of patients matched on both HER2 and HR status, and 94% of patients matched with the EMR on metastatic and recurrence status. When surgery and treatment information was included with these features, only 57% of patients matched across all these characteristics. Similar concordance was observed between the App questionnaire and EMR. Excluding the 21% of patients reporting “unsure” HER2 status improved the concordance to 85%. Overall concordance of recurrent or metastatic status was higher than for receptor status. Despite the discordance between EMR and patient-reported disease information, 97% of patients reported that they somewhat or strongly understood their cancer diagnosis. A similar pattern of concordance between the App questionnaire and EMR was observed among a real-world cohort of 636 patients using the Outcomes4Me App who provided medical record access. Conclusion: Self report of hormone receptor and HER2 status had limited concordance with the EMR, in contrast to a high degree of accuracy for self-report of metastatic disease. The limited accuracy of self-report suggests a need for improved patient education regarding their cancer characteristics and a need for caution when relying on self-report for clinical trials matching and targeted patient education. The use of a digital platform that integrates self-report with medical record access may help address these critical needs impacting patient empowerment and care.

Concordance Between App Questionnaire, Study Survey and EMR (% of patients)Disease Characteristic Matching CriteriaApp v. EMR (n=85)Survey v. EMR (n=107)App Real World Cohort (n=636)HER2 Status73%66%79%HR Status80%85%80%Combined Receptor Status67%62%73%Metastatic Status94%(n=79)97%(n=98)94%Surgery History83%(n=47)95%96%(n=310)Recurrent Status98%(n=48)97%(n=98)98%(n=411)Recurrent/Metastatic Status93%(n=42)94%(n=98)98%(n=411)Receptor/Recurrent Metastatic Status and Surgery History74%(n=33)57%(n=93)70%(n=201)

Citation Format: Steven J Isakoff, Eva Glieberman, Maya Said, Agnes H. Kwak, Emily A. O’Rourke, Amanda Stroiney, Laura Spring, Beverly Moy, Aditya Bardia, Nora Horick, Jeffrey Peppercorn. Accuracy of Patient Self-Reported Breast Cancer Disease Characteristics Compared to the Medical Record in a Trial of the Outcomes4MeDigital Health App [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 P4-12-08.

Abstract PD5-11: Pilot study to assess prolonged nightly fasting in breast cancer survivors (LONGFAST)

Background: Prior, retrospective analysis of nightly fasting among women with breast cancer suggests that fasting less than 13 hours per night may be associated with higher risk of breast cancer recurrence. Small studies suggest that fasting duration can influence inflammation, obesity, sleep, and other potential mediators of breast cancer recurrence risk. Prolonged overnight fasting is a simple, nonpharmacological behavioral intervention strategy that may be doable for most patients. We designed this pilot study to prospectively evaluate the feasibility of prolonged overnight fasting among breast cancer survivors. Methods: We designed a single-arm, pilot study to evaluate the feasibility of fasting for 13 hours overnight for a 12-week period among women with a history of early stage breast cancer (I to III) who had completed initial cancer therapy at least 6 months prior. Baseline and end of study assessments included measurements of body mass index (BMI), quality of life (QOL) (Functional Assessment of Cancer Therapy - General (FACT-G)), mood (Hospital Anxiety and Depression Scale (HADS)), fatigue (Functional Assessment of Chronic Illness Therapy (FACIT) - Fatigue), levels of physical activity (Godin Leisure-Time Exercise Questionnaire), and blood biomarkers (expanded lipid profile, hemoglobin A1c, C-reactive protein, interleukin-6, tumor necrosis factor alpha, leptin, adiponectin). Patient-reported outcome (PRO) surveys were also administered at 6 weeks. Feasibility was defined as ≥ 60% of participants documenting fasting in the food diary for 13 hours on at least 70% of nights during the study period. Changes in study measures from baseline were evaluated using Wilcoxon signed-rank tests. Results: Between July 2020 and January 2021, we enrolled 40 women with a history of breast cancer. Participants had a median age of 59.9 (range 34.9-76.3) and median time since diagnosis was 4.5 years (range 0.8-20.7). At baseline, BMI was normal (18.5-24.9) in 40.0%, overweight (25-29.9) in 37.5%, and obese (≥30) in 22.5%. Forty-two and a half percent had Stage I cancer, 42.5% stage II, and 15.0% stage III. Sixty-five percent were on hormonal therapy. Ninety-five percent of participants fasted ≥ 13 hours for at least 70% of study days (95% CI 83%-99%). At 6 weeks, there was a statistically significant improvement in anxiety (p=.0007). No other significant changes were seen in PROs. At 12 weeks, there were statistically significant improvements in BMI (p=.0072), anxiety (p=.0141), depression (p=.0048), and fatigue (p=.0105). There was no association between change in BMI during the study and baseline BMI category, age, or endocrine therapy. There was no significant change in overall QOL, physical activity levels, or blood biomarkers at 12 weeks. Conclusions: Prolonged overnight fasting is feasible in the breast cancer population and may improve BMI, mood, and fatigue without a detrimental effect on overall QOL. The data from this study support the need for a larger, longer randomized study of prolonged overnight fasting in the breast cancer population to further evaluate the effects on body composition, mood, QOL, metabolic markers, and risk of recurrence.

Table 1.Impact of Prolonged Overnight Fasting among Breast Cancer SurvivorsStudy AssessmentMedian at baselineMedian at 12 weeksMedian within-participant changep-valueBody Mass Index (kg/m2)26.4225.80-0.380.0072HADS - Depression1.001.00-1.000.0048HADS - Anxiety4.504.00-0.500.0141FACIT - Fatigue47.5049.821.000.0105FACT-G - Quality of Life95.2096.840.910.4933Physical Activity Level40.5039.000.000.3340Hemoglobin A1c (mg/dL)5.455.400.000.2758High-density lipoprotein (mg/dL)72.0073.00-2.000.4688Low-density lipoprotein (mg/dL)92.0099.001.000.5626Total Cholesterol (mg/dL)193.00192.003.000.6569C-reactive protein (mg/L)1.500.90-0.100.1043Interleukin-6 (pg/mL)2.001.90-0.300.1213Tumor Necrosis Factor α (pg/mL)0.740.74-0.050.2898Adiponectin (ug/mL)12.0012.000.000.0682Leptin (ng/mL)7.158.30-0.100.8418

Citation Format: Elizabeth K. O'Donnell, Yael N. Shapiro, Amy Comander, Steven J. Isakoff, Beverly Moy, Laura Spring, Seth Wander, Irene Kuter, Jennifer Shin, Jerry Younger, Michelle Specht, Chryssanthi Kourniotis, Carol Sullivan, Loren Winters, Nora Horick, Jeffrey Peppercorn. Pilot study to assess prolonged nightly fasting in breast cancer survivors (LONGFAST) [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 PD5-11.

Chemotherapy and Targeted Therapy for Patients With Human Epidermal Growth Factor Receptor 2-Negative Metastatic Breast Cancer That is Either Endocrine-Pretreated or Hormone Receptor-Negative: ASCO Guideline Update

PURPOSE

This guideline updates recommendations of the ASCO guideline on chemotherapy and targeted therapy for patients with human epidermal growth factor receptor 2-negative metastatic breast cancer (MBC) that is either endocrine-pretreated or hormone receptor (HR)-negative.

METHODS

An Expert Panel conducted a targeted systematic literature review guided by a signals approach to identify new, potentially practice-changing data that might translate into revised guideline recommendations.

RESULTS

The Expert Panel reviewed abstracts from the literature review and retained 14 articles.

RECOMMENDATIONS

Patients with triple-negative, programmed cell death ligand-1-positive MBC may be offered the addition of immune checkpoint inhibitor to chemotherapy as first-line therapy. Patients with triple-negative, programmed cell death ligand-1-negative MBC should be offered single-agent chemotherapy rather than combination chemotherapy as first-line treatment, although combination regimens may be offered for life-threatening disease. Patients with triple-negative MBC who have received at least two prior therapies for MBC should be offered treatment with sacituzumab govitecan. Patients with triple-negative MBC with germline BRCA mutations previously treated with chemotherapy may be offered a poly (ADP-ribose) polymerase inhibitor rather than chemotherapy. Patients with HR-positive human epidermal growth factor receptor 2-negative MBC for whom chemotherapy is being considered should be offered single-agent chemotherapy rather than combination chemotherapy, although combination regimens may be offered for highly symptomatic or life-threatening disease. Patients with HR-positive MBC with disease progression on an endocrine agent may be offered treatment with either endocrine therapy with or without targeted therapy or single-agent chemotherapy. Patients with HR-positive MBC with germline BRCA mutations no longer benefiting from endocrine therapy may be offered a poly (ADP-ribose) polymerase inhibitor rather than chemotherapy. No recommendation regarding when a patient's care should be transitioned to hospice or best supportive care alone is possible.Additional information is available at www.asco.org/breast-cancer-guidelines.

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

PURPOSE

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

EXPERIMENTAL DESIGN

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

RESULTS

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

CONCLUSIONS

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

TRIO-US B-12 TALENT: Phase II neoadjuvant trial evaluating trastuzumab deruxtecan with or without anastrozole for HER2-low, HR+ early stage breast cancer

TPS603

Background: Although patients with hormone receptor-positive (HR+)/HER2-negative breast cancer (BC) frequently respond clinically to neoadjuvant treatment, fewer than 10% achieve a pathologic complete response (pCR) with standard chemotherapy or endocrine therapy, even in combination with targeted agents such as CDK4/6 inhibitors. Thus, finding more effective therapies for this disease remains an area of unmet need. HER2 amplification is a known driver of endocrine resistance and HER2 protein may be expressed at a low level (IHC 1+ or 2+) in up to 60% of HR+ BC. Trastuzumab deruxtecan (DS-8201a, T-DXd) is a novel HER2-targeting antibody drug conjugate (ADC) that is FDA approved for HER2-positive metastatic BC and has demonstrated promising clinical efficacy in HER2-low BC with an objective response rate of ̃37%. The aim of TALENT (TRIO-US B-12) is to evaluate the clinical activity and toxicity of neoadjuvant T-DXd either alone or in combination with endocrine therapy in patients with HR+/HER2-low early BC. Methods: TRIO-US B-12 TALENT (NCT04553770) is an ongoing randomized, multicenter, open-label, two-stage, phase II neoadjuvant trial for participants with early stage, HR+, HER2-low expressing (1+ or 2+ by IHC) BC. Eligible participants include men and women with previously untreated, operable invasive BC greater than 2.0 cm (cT2) in size. Pts with recurrent or metastatic BC, or inflammatory BC are excluded. Pts are randomized 1:1 to receive six cycles of T-DXd (5.4 mg/kg IV q21 days) either alone or in combination with anastrozole (1 mg PO QD). Men and pre/peri menopausal women randomized to the anastrozole arm also receive standard of care GnRH agonist. Stratification factors include HER2 expression (1+ or 2+) and menopausal status. Tumor tissue is taken at baseline, cycle 1 day 17-21, and at surgery. Blood samples are taken at four time points for biomarker analysis. The primary endpoint is pCR rate (breast and lymph node) at definitive surgery. In stage I, 58 participants will be randomized (29/arm). If >2 participants in an arm achieve pCR, that arm will expand (stage II) to enroll an additional 15 participants (total of 44/arm). A pCR rate of >10% (5/44) would be considered favorable, warranting further evaluation of the treatment in a larger trial. Other endpoints include safety, changes in Ki67 expression, Residual Cancer Burden index, biomarker analysis (including serial cfDNA analysis), and health-related quality of life. As of January 2021, four participants have enrolled. Conclusions: To our knowledge this is the only ongoing study evaluating T-DXd with or without endocrine therapy for HR+, HER2-low breast cancer in the neoadjuvant setting. The study will shed light on clinical activity and biomarkers, which may guide larger confirmatory studies for patients with HR+, HER2-low early breast cancer. Clinical trial information: NCT04553770.

Feasibility of integrating the Outcomes4Me smartphone navigation application into the care of breast cancer patients (FIONA)

1570

Background: Patients diagnosed with breast cancer (BC) face complex decisions about their care and many studies have shown that improved patient engagement results in increased satisfaction and better outcomes. Patient engagement includes education, treatment option selection, symptom tracking and reporting, and clinical trial opportunities. We conducted a pilot study to determine the feasibility of introducing the Outcomes4Me patient engagement app into the standard of care experience of BC patients. Methods: This was a pilot study (NCT04262518) conducted at an academic medical center. Eligible patients had any subtype of stage 1-4 BC and were on any type of chemo-, hormonal-, targeted-, or radiation-therapy for BC during the study period. Participants downloaded the app on their smartphone and their app usage was evaluated. Surveys were administered at baseline and end of study. Clinicians caring for patients using the app were surveyed at the end of the study. The primary endpoint was feasibility, defined as at least 40% of patients engaging with the app at least 3 times over the 12-week study period. Additional endpoints included usability, satisfaction, correlation of patient reported data with the EHR, clinical trial matching, and patient experience. Results: Between June 2020 and December 2020, 107 patients enrolled; results are reported for 90 patients with complete data as of 1/24/21. Baseline demographics: median age 53 (range: 27-77); 90% White, 4% Black, 3% Asian; 66% had hormone positive/HER2-, 20% HER2+, and 13% triple negative BC; 31% had stage 4 disease. At study entry, 93% had never used an app to help with their disease or treatment options. Over the 12 week study period, 58% of patients engaged with the app at least 3 times, meeting the primary feasibility endpoint. Patients engaged with the app on average 5.5 days (range: 0-40) with 20% engaging on more than 10 days during the study. The mean System Usability Score was 71 (median = 76) and was similar across age groups. The 5 app features deemed most (‘somewhat’ or ‘very’) helpful were: background about their BC (76%), information about treatment options (74%), newsfeed about their BC (70%), symptom tracking (65%), and clinical trial information (65%). 53% said that the app helped them keep track of symptoms and 33% said they are more likely to explore or enroll in a clinical trial after using the app. Conclusions: Integration of the Outcomes4Me app into the care management of BC patients is feasible with acceptable usability. Our results suggest that use of a patient smartphone app may be helpful for many aspects of patient education and engagement for patients with BC. The results also suggest that this type of intervention can help patients better track their symptoms and make them aware of clinical trials, potentially facilitating the management of side effects and accelerating clinical trials recruitment. Clinical trial information: NCT04262518.

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

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

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

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

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

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

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

PURPOSE

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

PATIENTS AND METHODS

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

RESULTS

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

CONCLUSION

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

Effect of Eribulin With or Without Pembrolizumab on Progression-Free Survival for Patients With Hormone Receptor-Positive, ERBB2-Negative Metastatic Breast Cancer: A Randomized Clinical Trial

Importance

Prior studies have shown that only a small proportion of patients with hormone receptor (HR)-positive metastatic breast cancer (MBC) experience benefit from programmed cell death 1 (PD-1)/programmed cell death ligand 1 (PD-L1) inhibitors given as monotherapy. There are data suggesting that activity may be greater with combination strategies.

Objective

To compare the efficacy of eribulin plus pembrolizumab vs eribulin alone in patients with HR-positive, ERBB2 (formerly HER2)-negative MBC.

Design, Setting, and Participants

Multicenter phase 2 randomized clinical trial of patients with HR-positive, ERBB2-negative MBC who had received 2 or more lines of hormonal therapy and 0 to 2 lines of chemotherapy.

Interventions

Patients were randomized 1:1 to eribulin, 1.4 mg/m2 intravenously, on days 1 and 8 plus pembrolizumab, 200 mg/m2 intravenously, on day 1 of a 21-day cycle or eribulin alone. At time of progression, patients in the eribulin monotherapy arm could cross over and receive pembrolizumab monotherapy.

Main Outcomes and Measures

The primary end point was progression-free survival (PFS). Secondary end points were objective response rate (ORR) and overall survival (OS). Exploratory analyses assessed the association between PFS and PD-L1 status, tumor-infiltrating lymphocytes (TILs), tumor mutational burden (TMB), and genomic alterations.

Results

Eighty-eight patients started protocol therapy; the median (range) age was 57 (30-76) years, median (range) number of prior lines of chemotherapy was 1 (0-2), and median (range) number of prior lines of hormonal therapy was 2 (0-5). Median follow-up was 10.5 (95% CI, 0.4-22.8) months. Median PFS and ORR were not different between the 2 groups (PFS, 4.1 vs 4.2 months; hazard ratio, 0.80; 95% CI, 0.50-1.26; P = .33; ORR, 27% vs 34%, respectively; P = .49). Fourteen patients started crossover treatment with pembrolizumab; 1 patient experienced stable disease. All-cause adverse events occurred in all patients (grade ≥3, 65%) including 2 treatment-related deaths in the combination group, both from immune-related colitis in the setting of sepsis, attributed to both drugs. The PD-L1 22C3 assay was performed on archival tumor samples in 65 patients: 24 (37%) had PD-L1-positive tumors. Analysis indicated that PD-L1 status, TILs, TMB, and genomic alterations were not associated with PFS.

Conclusions and Relevance

In this randomized clinical trial of patients with HR-positive, ERBB2-negative MBC, the addition of pembrolizumab to eribulin did not improve PFS, ORR, or OS compared with eribulin alone in either the intention-to-treat or PD-L1-positive populations. Further efforts to explore the benefits of adding checkpoint inhibition to chemotherapy among less heavily pretreated patients are needed.

Trial Registration

ClinicalTrials.gov Identifier: NCT03051659.

Optimizing Radiation Therapy to Boost Systemic Immune Responses in Breast Cancer: A Critical Review for Breast Radiation Oncologists

Immunotherapy using immune checkpoint blockade has revolutionized the treatment of many types of cancer. Radiation therapy (RT)-particularly when delivered at high doses using newer techniques-may be capable of generating systemic antitumor effects when combined with immunotherapy in breast cancer. These systemic effects might be due to the local immune-priming effects of RT resulting in the expansion and circulation of effector immune cells to distant sites. Although this concept merits further exploration, several challenges need to be overcome. One is an understanding of how the heterogeneity of breast cancers may relate to tumor immunogenicity. Another concerns the need to develop knowledge and expertise in delivery, sequencing, and timing of RT with immunotherapy. Clinical trials addressing these issues are under way. We here review and discuss the particular opportunities and issues regarding this topic, including the design of informative clinical and translational studies.

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

PURPOSE

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

EXPERIMENTAL DESIGN

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

RESULTS

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

CONCLUSIONS

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

Pathologic evaluation of response to neoadjuvant therapy drives treatment changes and improves long-term outcomes for breast cancer patients

Systemic therapy for breast cancer may be given before (neoadjuvant) or after (adjuvant) surgery. When neoadjuvant systemic therapy is given, response to treatment can be evaluated. However, some prognostic information (for example, pathologic tumor size pretreatment) is then lost and pathologic evaluation of breast specimens after neoadjuvant therapy is more difficult. Pathologic complete response (pCR), defined as no invasive disease in the breast (ypT0/is or ypT0) and no disease in all sampled lymph nodes (ypN0), identifies patients with a lower risk of recurrence or death compared to those with residual disease. Multidisciplinary collaboration, marking of the tumor site and any lymph node involvement pretreatment, and access to specimen imaging to facilitate correlation of gross and microscopic findings are critical for accurate determination of pCR. For HER2-positive and triple negative tumors requiring systemic therapy, giving the treatment before surgery identifies a high-risk group of patients that can receive additional adjuvant therapy after surgery if a pCR is not achieved. Recent clinical trials have demonstrated that this approach reduced recurrence risk. More than ever, pathologic evaluation of response to neoadjuvant systemic therapy directs treatment received after surgery. Using a single standardized protocol for sampling of the post-neoadjuvant surgical specimen allows pathologists to ensure accurate determination of pCR or residual disease and quantify residual disease. Residual cancer burden (RCB) and AJCC stage provide complementary quantitative information about residual disease and prognosis.

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

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

Phase II study of adjuvant endocrine therapy with CDK 4/6 inhibitor, ribociclib, for localized ER+/HER2- breast cancer (LEADER)

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Background: Given the success of CDK 4/6 inhibitors for ER+/HER2- metastatic breast cancer, there is much interest in exploring these agents in early breast cancer to potentially reduce recurrence risk. However, tolerability and adherence are important considerations in the adjuvant setting. We evaluated the tolerability and adherence of adjuvant endocrine therapy with the CDK 4/6 inhibitor, ribociclib, in two different schedules, in a prospective phase II clinical trial. Methods: Eligible patients were those with localized stage I-III ER+ (≥ 10%), HER2- breast cancer who had completed surgery and were on adjuvant endocrine therapy with at least one year or more of treatment remaining. Patients were randomized to receive continuous ribociclib (400 mg daily of 28-day cycle; arm 1) or intermittent ribociclib (600 mg daily on days 1-21 of 28-day cycle; arm 2) for one year, in addition to an aromatase inhibitor (plus GnRH agonist if premenopausal). Toxicities were evaluated using CTCAE version 4.03. Adherence was monitored by review of patient diaries and pill count. Results: Of the 81 patients enrolled, 24 discontinued early. The table shows the current status of the patients based on treatment arm (data cut-off as of 1/31/20; updated results will be presented at meeting). A total of 8 serious adverse events (AEs) have occurred thus far: grade 3 transaminitis (1), grade 4 transaminitis (3), grade 3 colitis (1), grade 3 infection (2), and grade 4 lymphopenia (1). The most common grade 3 or greater AEs leading to study discontinuation thus far were transaminitis (8.6%), neutropenia (2.5%), and fatigue (2.5%). No patients discontinued early due to prolonged QTc. Adherence results will be reported at the meeting. Conclusions: Interim results demonstrate that while serious AEs with one year of adjuvant ribociclib are low, a number of patients discontinued adjuvant CDK 4/6 inhibitor. Tolerability and adherence patterns will need to be carefully considered with CDK 4/6 inhibitors in the adjuvant setting. Clinical trial information: NCT03285412 . [Table: see text]

Letrozole + ribociclib versus letrozole + placebo as neoadjuvant therapy for ER+ breast cancer (FELINE trial)

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Background: Ribociclib (R) + letrozole (L) is superior to L in metastatic breast cancer (BC). Preoperative endocrine prognostic index (PEPI) score 0 after neoadjuvant endocrine therapy (NET) is associated with low risk of relapse without chemotherapy in ER+ BC. On-therapy change in Ki-67 predicts adjuvant recurrence. FELINE is a biomarker-based multicenter randomized trial comparing changes in Ki-67 and PEPI between L+ Placebo (P) & L+R. Methods: Postmenopausal women with >2 cm or node+ ER+ HER2- BC were randomized 1:1:1 between L+P, L+R 400 mg continuous dose (Rc) and L+R 600 mg, 3 weeks on/1 week off - intermittent dose (Ri). Treatment was continued for six 28-day cycles. Core biopsies, blood samples were obtained at baseline, Day 14 cycle 1 (D14C1), and surgery. Clinical measurement, mammogram and US were obtained at baseline, surgery; MRI at baseline, week 8. Primary endpoint was rate of PEPI score 0 between L+P and L+R (i+c combined). Other endpoints were change in centrally performed Ki-67, complete cell cycle arrest (CCCA): Ki-67 <2.7%, clinical/imaging response, and difference in response & toxicity between the two R (Rc and Ri) arms. Results: From 2/2016 to 8/2018, 120 women were enrolled at 9 US centers. Thirty-eight were randomized to L+P and 82 to L+R groups (41 in Ri and Rc). Treatment groups were balanced at baseline. PEPI score of 0 was equal (25%) in L+P & L+R groups. CCCA at D14C1 was observed in 52% vs. 92% in L+P, L+R respectively (p < 0.0001). CCCA at surgery was observed in 63.3% vs. 71.4% in L+P, L+R respectively (p = NS). A significant increase in Ki-67 was observed between D14C1 and surgery in 66% vs. 33% in L+R, L+P respectively (p = 0.006). There was no difference in clinical, mammographic, US or MRI response between L+P and L+R. CCCA at D14C1 and surgery was similar in Ri & Rc arms. Grade >3 AEs were observed in 4 (10%) patients in L+P, 23 (56%) in L+Ri, 19 (46%) in L+Rc arms. Conclusions: Addition of R to L as NET did not result in more women with a PEPI score of 0. At D14C1 twice as many women on L+R had CCCA compared to L+P (92% vs 52%). However, significantly more women on L+R had increased proliferation between D14C1 and surgery , resulting in similar CCCA at surgery. Correlative studies are being performed to determine mechanisms of on-therapy acquired resistance to ribociclib. Continuous and intermittent doses of R have similar efficacy, toxicity. Clinical trial information: NCT02712723 . [Table: see text]

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

1066

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

Factors associated with frequent insomnia among breast cancer survivors

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Background: Insomnia is common among breast cancer (BC) survivors and often goes unrecognized and untreated. We sought to evaluate the association between frequent insomnia and potentially modifiable contributing factors to inform development of a comprehensive clinical program to address insomnia among patients with breast cancer. Methods: We adapted a 1-page survey from the National Comprehensive Cancer Network Guidelines for Survivorship, which was administered to BC survivors at oncology or primary care follow-up visits at our academic center and community based sites. The survey included 23 plain-language statements regarding symptoms, lifestyle concerns, and financial worries. Patients reported the frequency of concerns using a 5-point Likert scale (0 = never to 5 = always). We evaluated the frequency of insomnia and association between insomnia and 6 common concerns hypothesized to contribute among this population: emotional distress, fatigue, pain, hot flashes, fear of cancer recurrence, and healthcare-related financial stress. Prevalence of symptoms was dichotomized, grouping “very often” and “always” as “frequent”, and “sometimes,” “rarely”, and “never” as “infrequent”. Descriptive analysis was performed and associations between insomnia and other concerns were evaluated with Fisher’s exact test. Results: Among 192 patients (median age 59, range 34-92), 46 (24%) reported frequent insomnia (“I have problems falling or staying asleep”). Most patients (58%) reported experiencing insomnia at least “sometimes”, while 20% answered “rarely” and 23% “never”. Overall, 14% of survivors reported frequent anxiety/depression, 15% fatigue, 27% pain, 19% hot flashes, and 23% fear of recurrence. Only 6% of patients reported frequent financial worries due to healthcare costs. Emotional distress (p=0.016), fatigue (p≤0.001), pain (p≤0.001), hot flashes (p=0.017), and fear of recurrence (p≤0.01) were each associated with frequent insomnia. Conclusions: BC survivors who experience frequent insomnia are more likely to report emotional distress, fatigue, pain, hot flashes, and fear of recurrence, compared to those with infrequent insomnia. A clinical program designed for the management of insomnia may benefit from targeting these potentially contributing factors.

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

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

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

Abstract P3-09-16: Fecal microbiome and association with outcomes among patients (pts) receiving eribulin (E) +/- pembrolizumab (P) for hormone receptor positive (HR+) metastatic breast cancer (MBC)

Background: Recent studies in murine models and humans suggest that modulation of the gut microbiome may enhance response to immune checkpoint blockade in different cancer types. However, little is known about the landscape of gut microbiome in pts with HR+ MBC and its influence on response to chemotherapy and immunotherapy.Methods: A randomized phase 2 trial of E +/- P for pts with HR+ MBC (n= 88) was conducted. The results of this study have been previously presented and found the addition of P did not result in an improvement in progression-free survival (PFS). Fecal samples were prospectively collected (baseline (BL), after 2 cycles of therapy (C2), and end of treatment (EOT)) in a subset of pts (E+P, n = 12; E, n = 11) in order to evaluate if microbiome was associated with response (partial response [PR], stable disease [SD], and progressive disease [PD]), PFS, and overall survival (OS). 16S rRNA gene sequencing was performed to characterize the diversity and composition of fecal microbiome. Results: A total 23 pts provided 23 BL, 22 C2, and 5 EOT fecal specimens for microbiome profiling. 16S(v3-4) rRNA gene data was successfully generated for all samples and the dataset was rarefied to 24,743 reads for analysis. Overall, the variability in the composition and structure of the fecal microbiome was significantly driven by each individual (p&lt;0.001) more than any other variable studied. This effect was observed across all timepoints collected. At BL, subjects randomized to receive E+P and E did not show any differences in composition (p = 0.715) and structure (p = 0.457) of the fecal microbiome. The major genera identified in E+P and E groups were Bacteroides, 37.9% vs. 41.56%; Faecalibacterium 9.9% vs. 4.4%, and Blautia 4.9% vs. 2.9%, respectively. These abundances were observed at a similar level in the C2 sample. Overall, subjects receiving E had a marked increase in Faecalibacterium from 6.4% at BL to 21.2% at C2 and a decrease in Akkermansia from BL (8.5%) to C2 (&lt;1%). Among those pts receiving E who achieved a PR, the abundance of Faecalibacterium increased from BL (4.3%) to C2 (13.9%), while the levels remained unchanged in those achieving SD. These shifts in abundance were not observed in the group receiving E+P. Subjects with PFS below the median had comparable alpha-diversity scores to those above the median in both arms of the study. Specifically, the number of Operational Taxonomic Units (OTUs) observed at BL in pts receiving E+P with PFS above and below the median were 563 and 663, respectively. When looking at the differences between BL and C2, OTUs decreased slightly to 513 and 637, respectively. Similar results were observed in pts receiving E. Among pts with PFS time below the median receiving E, there was a decrease in Akkermansia from BL (5.7%) to C2 (&lt;1%). Pts with OS below the median had comparable alpha-diversity scores at BL to those above the median OS in both arms of the study. Pts with OS above the median receiving E experienced a decrease in the abundance of Akkermansia from BL (5.3%) to C2 (2.4%).

Conclusion: The composition and structure of the fecal microbiome identified in this study were found to be associated primarily with the pt rather than with any of the variables studied including type of treatment and outcome. Although the fecal microbiome from all pts randomized were indistinguishable at BL, shifts in the abundance of certain types of bacteria like Faecalibacterium and Akkermansia were observed from BL to C2. These shifts were characteristic of pts receiving E but not of those receiving E+P. Although this study is limited by the small sample size in each arm, these findings warrant further evaluation in a larger population to interrogate if the composition and metabolic potential of the fecal microbiome can be used as a predictor of benefit to treatment.

Citation Format: Romualdo Barroso de Sousa, Nadim Ajami, Tanya E Keenan, Chelsea Andrews, Jessica L Pittenger, Gerburg Wulf, Laura Spring, Ian E Krop, Eric P Winer, Elizabeth A Mittendorf, Sara M Tolaney. Fecal microbiome and association with outcomes among patients (pts) receiving eribulin (E) +/- pembrolizumab (P) for hormone receptor positive (HR+) metastatic breast cancer (MBC) [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-09-16.

Abstract P4-09-06: Brain metastases (BM) in patients with metastatic breast cancer (MBC) and circulating cell-free DNA (cfDNA) somatic BRCA mutations

Background: BM in MBC patients cause significant morbidity and mortality. BRCA1 germline mutations have previously been shown to be associated with an increased risk of developing BM (Lee et al, 2011), with an incidence as high as 15% (Zavitsanos et al, 2016). We previously reported that a subset of MBC patients may have somatic BRCA mutations in the absence of germline BRCA mutations (Vidula N, SABCS, 2017). In this study, we evaluated the incidence and clinical characteristics of BM in MBC patients with somatic BRCA mutations detected by cfDNA.

Methods: MBC patients with somatic BRCA1 or 2 mutations detected by cfDNA (Guardant360TM, next generation sequencing, 73 gene panel; mutations classified as somatic by Guardant360TM) with at least 4 months of follow-up post-testing at an academic institution were identified. From this cohort, we identified patients who developed BM post cfDNA testing. A retrospective review of medical records and Guardant360TM reports was conducted to identify demographics, tumor subtype, type of cfDNA BRCA mutation, whether the BRCA mutation was known to be pathogenic, germline BRCA mutation status, mutant allele fraction (MAF), clonality (MAF ratio of BRCA mutation/gene mutation with highest MAF ≥ 0.25 for clonal, and &lt;0.25 for subclonal) and the coexisting genomic environment. Clinical and genomic features of BM and non-BM patients (patients without BM) were compared using a chi-squared test for categorical variables and Wilcoxon rank-sum test for continuous variables. Brain tumor tissue from available cases of BM patients was used to evaluate somatic BRCA mutation status on the tumor tissue and correlated with cfDNA results.

Results: Of 36 MBC patients with somatic BRCA mutations, 9 (25%) developed BM and 27 (75%) did not have BM (non-BM). The median time to development of BM was 6.7 months after cfDNA testing. Of the BM patients, 5 (56%) had triple-negative (TN) and 4 (44%) had hormone receptor positive (HR+)/HER2- MBC in comparison with the non-BM cases where 5 (19%) had TN, 19 (70%) had HR+/HER2-, and 3 (11%) had HER2+ MBC. Very few patients (1 BM and 2 non-BM) had known co-existing separate germline BRCA mutations (rest not known BRCA carriers confirmed by negative germline testing and/or absence of family history suggestive of a germline BRCA phenotype). The median age at MBC diagnosis was similar for BM and non-BM patients (57 years). PIK3CA and TP53 mutations were commonly seen in both BM and non-BM cases. Additionally, MYC, EGFR, and CCNE1 mutations were commonly seen in BM cases. As outlined in Table 1, among patients with BM, the somatic BRCA mutations were commonly BRCA1, clonal, known to be pathogenic (56%), and present at a higher MAF, but these findings did not reach statistical significance possibly due to the small sample size. Brain tumor tissue mutation status in BM patients and correlation with cfDNA results will be presented at the meeting.

Conclusions: We observed a relatively high incidence (25%) of BM in MBC patients with somatic BRCA mutations detectable by cfDNA, which were often known to be pathogenic mutations (56%), and often associated with co-existing MYC, EGFR, and CCNE1 mutations. Further research using a larger cohort with adequate statistical power is needed to validate these findings, and may help identify MBC patients at risk for BM using a liquid biopsy.

Table 1.Characteristic BMNon-BMPrior anthracycline and/or platinum6 (67%)16 (59%)Type of somatic BRCA mutationBRCA16 (67%)11 (41%)BRCA22 (22%)15 (56%)BRCA1 and 21 (11%)1 (4%)Median BRCA MAF0.40.17ClonalityClonal6 (67%)13 (48%)Subclonal3 (33%)14 (52%)Mutation known to be pathogenic5 (56%)7 (26%)Common co-existing mutationsPIK3CA5 (56%)12 (44%)TP535 (56%)15 (56%)MYC5 (56%)8 (30%)EGFR5 (56%)8 (30%)CCNE15 (56%)6 (22%)KIT3 (33%)5 (19%)

Citation Format: Neelima Vidula, Andrzej Niemierko, Giuliana Malvarosa, Priscilla Brastianos, Erica Blouch, Kristen Shannon, Steven Isakoff, Seth Wander, Laura Spring, Jerry Younger, Kristin Price, Beverly Moy, Dejan Juric, Leif Ellisen, Aditya Bardia. Brain metastases (BM) in patients with metastatic breast cancer (MBC) and circulating cell-free DNA (cfDNA) somatic BRCA mutations [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 P4-09-06.

Blood-based monitoring identifies acquired and targetable driver HER2 mutations in endocrine-resistant metastatic breast cancer

Plasma genotyping identifies potentially actionable mutations at variable mutant allele frequencies, often admixed with multiple subclonal variants, highlighting the need for their clinical and functional validation. We prospectively monitored plasma genotypes in 143 women with endocrine-resistant metastatic breast cancer (MBC), identifying multiple novel mutations including HER2 mutations (8.4%), albeit at different frequencies highlighting clinical heterogeneity. To evaluate functional significance, we established ex vivo culture from circulating tumor cells (CTCs) from a patient with HER2-mutant MBC, which revealed resistance to multiple targeted therapies including endocrine and CDK 4/6 inhibitors, but high sensitivity to neratinib (IC50: 0.018 μM). Immunoblotting analysis of the HER2-mutant CTC culture line revealed high levels of HER2 expression at baseline were suppressed by neratinib, which also abrogated downstream signaling, highlighting oncogenic dependency with HER2 mutation. Furthermore, treatment of an index patient with HER2-mutant MBC with the irreversible HER2 inhibitor neratinib resulted in significant clinical response, with complete molecular resolution of two distinct clonal HER2 mutations, with persistence of other passenger subclones, confirming HER2 alteration as a driver mutation. Thus, driver HER2 mutant alleles that emerge during blood-based monitoring of endocrine-resistant MBC confer novel therapeutic vulnerability, and ex vivo expansion of viable CTCs from the blood circulation may broadly complement plasma-based mutational analysis in MBC.

Trastuzumab emtansine (T-DM1) and ribociclib, an oral inhibitor of cyclin dependent kinase 4 and 6 (CDK 4/6), for patients with metastatic HER2-positive breast cancer

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Background: Current therapeutic efforts in the management of HER2+ MBC focus on targeting the HER receptor family, however co-inhibition of targets downstream of the HER2 pathway, such as cyclin D-CDK 4/6, could enhance therapeutic efficacy. We conducted a phase 1b study of the CDK4/6 inhibitor ribociclib and T-DM1 in patients (pts) with HER2+ MBC. The primary objective was to determine the recommended phase 2 dose (RP2D) of ribociclib plus T-DM1. Secondary objectives included safety, PK assessments, and efficacy. Methods: Pts with HER2+ MBC who previously received at least 1 taxane and trastuzumab-containing regimen in any setting were eligible. Pts with previous CDK4/6 inhibitor exposure, QTcF > 450msec, or unstable brain metastases were excluded. Ribociclib was given orally for 2 weeks of a 21-day cycle (days 8-21), with T-DM1 given at 3.6 mg/kg every 3 weeks on day 1. A standard 3+3 dose escalation design was used to evaluate various doses of ribociclib in combination with T-DM1 to determine the RP2D. Results: From 5/2016 – 10/2018, 10 pts (8/10 ER+) were enrolled with a median age of 53 (38-72) and median of 1 (0-2) prior therapies for MBC. During dose-escalation, pts received doses of 300 mg (n = 3), 400 mg (n = 3), 500 mg (n = 3), and 600 mg (n = 1). No DLTs were observed. The most common treatment related grade 3 or higher AEs were neutropenia (50%), infection (20%), anemia (10%), and thrombocytopenia (10%). 4/10 pts had dose reductions due to toxicity. The average concentration of ribociclib at steady state was similar at each dose level, ranging from 273 to 413 ng/mL. Among 9 evaluable pts, the ORR was 33% (3/9) and the other 6 pts had stable disease. After a median follow-up time of 10.9 months, the median PFS was 12.5 months (95% CI [10.5. 20.9]). Biomarker results will be presented at the meeting. Conclusions: Co-targeting HER2 and CDK4/6 with the combination of ribociclib with T-DM1 was well tolerated with evidence of clinical activity. Based on PK analysis and dose reductions, 400 mg is the RP2D. Further evaluation is warranted for patients with HER2+ MBC. Clinical trial information: NCT02657343.