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Background: Datopotamab deruxtecan (Dato-DXd) is an antibody-drug conjugate (ADC) consisting of a humanized anti-TROP2 IgG1 monoclonal antibody covalently linked to a highly potent topoisomerase I (Topo I) inhibitor payload via a stable, tumor-selective, tetrapeptide-based cleavable linker. Dato-DXd demonstrated compelling single-agent antitumor activity in heavily pretreated patients (pts) with metastatic triple-negative BC (Krop, SABCS 2021). This is the first report of results from the TROPION-PanTumor01 study in pts with unresectable or metastatic hormone receptor–positive (HR+)/human epidermal growth factor receptor 2–negative (HER2−; including HER2-low and HER2-zero) BC. Methods: TROPION-PanTumor01 (NCT03401385) is a phase 1, multicenter, open-label, 2-part dose-escalation/expansion study evaluating Dato-DXd in previously treated pts with solid tumors. Based on previous clinical findings and exposure-response results from pts with NSCLC, Dato-DXd 6 mg/kg IV Q3W is being evaluated in pts with unresectable or metastatic HR+/HER2− BC that progressed on standard therapies. The primary objectives were safety and tolerability. Tumor responses, including ORR (complete response [CR] + partial response [PR]) and DCR (CR + PR + stable disease [SD]), were assessed per RECIST version 1.1 by blinded independent central review. Results: As of the April 29, 2022, data cutoff, 41 pts had received Dato-DXd (median follow-up, 10.9 mo [range, 7-13]); 9 pts were ongoing. The primary cause of treatment discontinuation was disease progression (63%; progressive disease [PD] or clinical progression). Median age was 57 y (range, 33-75); 54% had de novo metastatic disease. Pts were heavily pretreated (Table) with a median of 5 (range, 3-10) prior regimens in the advanced setting; 95% had prior CDK4/6i (adjuvant/metastatic). Median time from initial treatment for metastatic disease to the first dose of Dato-DXd was 42.7 mo (range, 10.2-131.1). Treatment-emergent adverse events (TEAEs; all cause) were observed in 98% (any grade) and 41% (grade ≥3) of pts. Most common TEAEs (any grade, grade ≥3) were stomatitis (80%, 10%), nausea (56%, 0%), fatigue (46%, 2%), and alopecia (37%, 0%). Serious TEAEs were observed in 6 pts (15%); 1 pt died due to dyspnea, which was not considered to be treatment related. Dose reductions occurred in 5 pts due to stomatitis (n=3), fatigue (n=2), keratitis (n=1), and decreased appetite (n=1) (>1 AE per pt); 14 pts had treatment delayed due to stomatitis (n=8), retinopathy (n=1), dysphagia (n=1), fatigue (n=1), malaise (n=1), COVID-19 (n=1), cellulitis (n=1), urinary tract infection (n=1), decreased lymphocyte count (n=1), and nasal congestion (n=1; >1 AE per pt). Three pts discontinued treatment due to keratitis (n=1) and pneumonitis (n=2); 1 case of pneumonitis was adjudicated as grade 2 drug-related interstitial lung disease. The ORR was 29% (11 confirmed PRs; 1 pending confirmation), the DCR was 85% (35/41), and the clinical benefit rate (CR + PR + SD ≥6 mo) was 41% (17/41). Conclusions: Dato-DXd demonstrated a manageable safety profile and encouraging antitumor activity, with high disease control in heavily pretreated pts, the majority having received prior CDK4/6i. Based on these findings, the TROPION-Breast01 (NCT05104866) randomized phase 3 study comparing 2L+ Dato-DXd vs investigator’s choice chemotherapy is currently enrolling pts with HR+/HER2− BC. Prior Therapies in the Adjuvant or Metastatic Setting Citation Format: Funda Meric-Bernstam, Ian Krop, Dejan Juric, Takahiro Kogawa, Erika Hamilton, Alexander I. Spira, Toru Mukohara, Takuya Tsunoda, Senthil Damodaran, Jonathan Greenberg, Wen Gu, Fumiaki Kobayashi, Hong Zebger-Gong, Yui Kawasaki, Rie Wong, Aditya Bardia. PD13-08 Phase 1 TROPION-PanTumor01 Study Evaluating Datopotamab Deruxtecan (Dato-DXd) in Unresectable or Metastatic Hormone Receptor–Positive/HER2–Negative Breast Cancer (BC) [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD13-08.

Background: PARP inhibitors are currently approved for the treatment of germline BRCA1/2 mutant metastatic breast cancer (MBC), which accounts for 5-10% of breast cancer. We hypothesize that a PARP inhibitor may also have efficacy in somatic BRCA1/2 mutant MBC, expanding the potential clinical applicability of PARP inhibitors. We previously demonstrated that somatic BRCA1/2 mutations can be identified by both cell-free DNA and tumor tissue genotyping in a subset of patients with MBC who are not germline BRCA1/2 carriers. Furthermore, a PARP inhibitor was demonstrated to induce cell growth inhibition in a circulating tumor cell culture model generated from a patient with pathogenic somatic BRCA1 mutant MBC (Vidula, Dubash, CCR, 2020). In this trial, we are evaluating the efficacy of a PARP inhibitor in somatic BRCA1/2 mutant MBC. Trial Design: This phase II investigator-initiated clinical trial is enrolling 30 patients with somatic BRCA1/2 mutant MBC identified via cell-free DNA or tumor tissue genotyping. Patients are treated with talazoparib, a PARP inhibitor, until disease progression. At baseline and every 3 months, patients undergo CT chest, abdomen, and pelvis, and a bone scan for disease assessment. Patients undergo blood collection at baseline for the Cancer Risk B (CR-B) assay, a novel flow variant assay to assess double-strand break repair mutations in circulating blood cells (Syeda, 2017) and monthly blood collection for cell-free DNA analysis to evaluate changes in the genomic environment. Eligibility Criteria: Patients with MBC with a pathogenic somatic BRCA1/2 mutation identified by cell-free DNA or tumor tissue genotyping are eligible. Both patients with triple-negative breast cancer (≥ 1 prior chemotherapy) or hormone receptor positive/HER2- MBC (≥ 1 prior hormone therapy) are eligible. Patients should not be known germline BRCA1/2 carriers. There is no limit on prior therapies including receipt of a prior platinum (in the absence of disease progression on prior platinum). A prior PARP inhibitor is not allowed. Adequate performance status and organ function are needed. Specific Aims: Primary aim is progression-free survival (PFS) assessed by RECIST 1.1. Secondary aims include objective response rate and toxicity assessed by NCI CTCAE v 5.0. Exploratory aims include assessing impact of BRCA1/2 reversion mutations in cell-free DNA, studying serial changes in BRCA1/2 mutant allelic frequency in cell-free DNA, comparing pre- and post-treatment cell-free DNA results to identify changes in the genomic environment, assessing the CR-B assay positivity rate, and correlating these biomarker analyses with patient response. Statistical Methods: This study uses a two-stage design with 80% power to demonstrate that talazoparib is associated with “success” (PFS > 12 weeks) in 53% patients (4% alpha). Accrual: This study (NCT03990896) is open at Massachusetts General Hospital, MD Anderson, University of California San Francisco, and Emory, with pending activation at Northwestern, Cornell, and Vanderbilt. Five patients are enrolled as of 7/2022. Funding: This study is supported by a Pfizer ASPIRE award and Conquer Cancer Foundation of ASCO–Breast Cancer Research Foundation- Career Development Award. Contact information: Neelima Vidula, MD, Massachusetts General Hospital, nvidula@mgh.harvard.edu Citation Format: Neelima Vidula, Senthil Damodaran, Erica L. Blouch, Nora Horick, Nathan Royce Ruffle-Deignan, Manali Bhave, Ami N. Shah, Leticia Varella, Vandana Abramson, Joseph Sparano, Leif Ellisen, Ishraq Alim, Harry Ostrer, Hope Rugo, Aditya Bardia. Phase II study of talazoparib, a PARP inhibitor, in somatic BRCA1/2 mutant metastatic breast cancer identified by cell-free DNA or tumor tissue genotyping [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT1-11-01.

High stromal tumor-infiltrating lymphocytes (sTILs) are associated with improved pathologic complete response (pCR) in triple-negative breast cancer (TNBC). We hypothesize that integrating high sTILs and additional clinicopathologic features associated with pCR could enhance our ability to predict the group of patients on whom treatment de-escalation strategies could be tested. In this prospective early-stage TNBC neoadjuvant chemotherapy study, pretreatment biopsies from 408 patients were evaluated for their clinical and demographic features, as well as biomarkers including sTILs, Ki-67, PD-L1 and androgen receptor. Multivariate logistic regression models were developed to generate a computed response score to predict pCR. The pCR rate for the entire cohort was 41%. Recursive partitioning analysis identified ≥20% as the optimal cutoff for sTILs to denote 35% (143/408) of patients as having high sTILs, with a pCR rate of 59%, and 65% (265/408) of patients as having low sTILs, with a pCR rate of 31%. High Ki-67 (cutoff > 35%) was identified as the only predictor of pCR in addition to sTILs in the training set. This finding was verified in the testing set, where the highest computed response score encompassing both high sTILa and high Ki-67 predicted a pCR rate of 65%. Integrating Ki67 and sTIL may refine the selection of early stage TNBC patients for neoadjuvant clinical trials evaluating de-escalation strategies.

PURPOSE To update recommendations on appropriate use of breast cancer biomarker assay results to guide adjuvant endocrine and chemotherapy decisions in early-stage breast cancer. METHODS An updated literature search identified randomized clinical trials and prospective-retrospective studies published from January 2016 to October 2021. Outcomes of interest included overall survival and disease-free or recurrence-free survival. Expert Panel members used informal consensus to develop evidence-based recommendations. RESULTS The search identified 24 studies informing the evidence base. RECOMMENDATIONS Clinicians may use Onco type DX, MammaPrint, Breast Cancer Index (BCI), and EndoPredict to guide adjuvant endocrine and chemotherapy in patients who are postmenopausal or age > 50 years with early-stage estrogen receptor (ER)–positive, human epidermal growth factor receptor 2 (HER2)–negative (ER+ and HER2–) breast cancer that is node-negative or with 1-3 positive nodes. Prosigna and BCI may be used in postmenopausal patients with node-negative ER+ and HER2– breast cancer. In premenopausal patients, clinicians may use Onco type in patients with node-negative ER+ and HER2– breast cancer. Current data suggest that premenopausal patients with 1-3 positive nodes benefit from chemotherapy regardless of genomic assay result. There are no data on use of genomic tests to guide adjuvant chemotherapy in patients with ≥ 4 positive nodes. Ki67 combined with other parameters or immunohistochemistry 4 score may be used in postmenopausal patients without access to genomic tests to guide adjuvant therapy decisions. BCI may be offered to patients with 0-3 positive nodes who received 5 years of endocrine therapy without evidence of recurrence to guide decisions about extended endocrine therapy. None of the assays are recommended for treatment guidance in individuals with HER2-positive or triple-negative breast cancer. Treatment decisions should also consider disease stage, comorbidities, and patient preferences. Additional information is available at www.asco.org/breast-cancer-guidelines .

Activating mutations in PIK3CA are observed across multiple tumor types. The NCI-MATCH (EAY131) is a tumor-agnostic platform trial that enrolls patients to targeted therapies on the basis of matching genomic alterations. Arm Z1F evaluated copanlisib, an α and δ isoform–specific phosphoinositide 3-kinase (PI3K) inhibitor, in patients with PIK3CA mutations (with or without PTEN loss). PATIENTS AND METHODS: Patients received copanlisib (60 mg intravenous) once weekly on days 1, 8, and 15 in 28-day cycles until progression or toxicity. Patients with KRAS mutations, human epidermal growth factor receptor 2–positive breast cancers, and lymphomas were excluded. The primary end point was centrally assessed objective response rate (ORR); secondary end points included progression-free survival, 6-month progression-free survival, and overall survival. RESULTS: Thirty-five patients were enrolled, and 25 patients were included in the primary efficacy analysis as prespecified in the Protocol. Multiple histologies were enrolled, with gynecologic (n = 6) and gastrointestinal (n = 6) being the most common. Sixty-eight percent of patients had ≥ 3 lines of prior therapy. The ORR was 16% (4 of 25, 90% CI, 6 to 33) with P = .0341 against a null rate of 5%. The most common reason for protocol discontinuation was disease progression (n = 17, 68%). Grade 3/4 toxicities observed were consistent with reported toxicities for PI3K pathway inhibition. Sixteen patients (53%) had grade 3 toxicities, and one patient (3%) had grade 4 toxicity (CTCAE v5.0). Most common toxicities include hyperglycemia (n = 19), fatigue (n = 12), diarrhea (n = 11), hypertension (n = 10), and nausea (n = 10). CONCLUSION: The study met its primary end point with an ORR of 16% (P = .0341) with copanlisib showing clinical activity in select tumors with PIK3CA mutation in the refractory setting.

Table S6

Purpose:Metastatic breast cancer (MBC) is not curable and there is a growing interest in personalized therapy options. Here we report molecular profiling of MBC focusing on molecular evolution in actionable alterations.Experimental Design:Sixty-two patients with MBC were included. An analysis of DNA, RNA, and functional proteomics was done, and matched primary and metastatic tumors were compared when feasible.Results:Targeted exome sequencing of 41 tumors identified common alterations in TP53 (21; 51%) and PIK3CA (20; 49%), as well as alterations in several emerging biomarkers such as NF1 mutations/deletions (6; 15%), PTEN mutations (4; 10%), and ARID1A mutations/deletions (6; 15%). Among 27 hormone receptor–positive patients, we identified MDM2 amplifications (3; 11%), FGFR1 amplifications (5; 19%), ATM mutations (2; 7%), and ESR1 mutations (4; 15%). In 10 patients with matched primary and metastatic tumors that underwent targeted exome sequencing, discordances in actionable alterations were common, including NF1 loss in 3 patients, loss of PIK3CA mutation in 1 patient, and acquired ESR1 mutations in 3 patients. RNA sequencing in matched samples confirmed loss of NF1 expression with genomic NF1 loss. Among 33 patients with matched primary and metastatic samples that underwent RNA profiling, 14 actionable genes were differentially expressed, including antibody–drug conjugate targets LIV-1 and B7-H3.Conclusions:Molecular profiling in MBC reveals multiple common as well as less frequent but potentially actionable alterations. Genomic and transcriptional profiling demonstrates intertumoral heterogeneity and potential evolution of actionable targets with tumor progression. Further work is needed to optimize testing and integrated analysis for treatment selection.

Supplementary Figures 1-5

Supplementary Tables S1-5 and Supplementary Fig. S1

Purpose:Increasing tumor-infiltrating lymphocytes (TIL) is associated with higher rates of pathologic complete response (pCR) to neoadjuvant therapy (NAT) in patients with triple-negative breast cancer (TNBC). However, the presence of TILs does not consistently predict pCR, therefore, the current study was undertaken to more fully characterize the immune cell response and its association with pCR.Experimental Design:We obtained pretreatment core-needle biopsies from 105 patients with stage I–III TNBC enrolled in ARTEMIS (NCT02276443) who received NAT from Oct 22, 2015 through July 24, 2018. The tumor-immune microenvironment was comprehensively profiled by performing T-cell receptor (TCR) sequencing, programmed death-ligand 1 (PD-L1) IHC, multiplex immunofluorescence, and RNA sequencing on pretreatment tumor samples. The primary endpoint was pathologic response to NAT.Results:The pCR rate was 40% (42/105). Higher TCR clonality (median = 0.2 vs. 0.1, P = 0.03), PD-L1 positivity (OR: 2.91, P = 0.020), higher CD3+:CD68+ ratio (median = 14.70 vs. 8.20, P = 0.0128), and closer spatial proximity of T cells to tumor cells (median = 19.26 vs. 21.94 μm, P = 0.0169) were associated with pCR. In a multivariable model, closer spatial proximity of T cells to tumor cells and PD-L1 expression enhanced prediction of pCR when considered in conjunction with clinical stage.Conclusions:In patients receiving NAT for TNBC, deep immune profiling through detailed phenotypic characterization and spatial analysis can improve prediction of pCR in patients receiving NAT for TNBC when considered with traditional clinical parameters.

PURPOSE Activating mutations in PIK3CA are observed across multiple tumor types. The NCI-MATCH (EAY131) is a tumor-agnostic platform trial that enrolls patients to targeted therapies on the basis of matching genomic alterations. Arm Z1F evaluated copanlisib, an α and δ isoform–specific phosphoinositide 3-kinase (PI3K) inhibitor, in patients with PIK3CA mutations (with or without PTEN loss). PATIENTS AND METHODS Patients received copanlisib (60 mg intravenous) once weekly on days 1, 8, and 15 in 28-day cycles until progression or toxicity. Patients with KRAS mutations, human epidermal growth factor receptor 2–positive breast cancers, and lymphomas were excluded. The primary end point was centrally assessed objective response rate (ORR); secondary end points included progression-free survival, 6-month progression-free survival, and overall survival. RESULTS Thirty-five patients were enrolled, and 25 patients were included in the primary efficacy analysis as prespecified in the Protocol. Multiple histologies were enrolled, with gynecologic (n = 6) and gastrointestinal (n = 6) being the most common. Sixty-eight percent of patients had ≥ 3 lines of prior therapy. The ORR was 16% (4 of 25, 90% CI, 6 to 33) with P = .0341 against a null rate of 5%. The most common reason for protocol discontinuation was disease progression (n = 17, 68%). Grade 3/4 toxicities observed were consistent with reported toxicities for PI3K pathway inhibition. Sixteen patients (53%) had grade 3 toxicities, and one patient (3%) had grade 4 toxicity (CTCAE v5.0). Most common toxicities include hyperglycemia (n = 19), fatigue (n = 12), diarrhea (n = 11), hypertension (n = 10), and nausea (n = 10). CONCLUSION The study met its primary end point with an ORR of 16% ( P = .0341) with copanlisib showing clinical activity in select tumors with PIK3CA mutation in the refractory setting.

Cyclin-dependent-kinase-4/6 inhibitor (CDK4/6i) plus endocrine therapy (ET) is standard of care for patients with advanced hormone receptor (HR)-positive, HER2-negative breast cancer (BC). The Breast Medical Oncology database at MD Anderson Cancer Center (MDACC) was analyzed to assess effectiveness of the CDK4/6i palbociclib plus ET compared to ET alone. From a total of 5402 advanced HR+ HER2- BC patients referred to MDACC between 1997 and 2020, we identified eligible patients who received palbociclib in combination with first-line (n = 778) and second-line (n = 410) ET. We further identified "control" patients who received ET alone in the first-line (n = 2452) and second-line (n = 1183) settings. Propensity score matching analysis was conducted to balance baseline demographic and clinical characteristics between palbociclib and control cohorts to assess the effect of palbociclib treatment on progression-free survival (PFS) and overall survival (OS). For propensity-matched-cohort in the first-line setting (n = 708), palbociclib group had significantly longer median PFS (17.4 vs 11.1 months; P .0001) compared to controls. Median OS (44.3 vs 40.2 months) did not show a statistically significant benefit in the first line setting. However, in the second-line setting, with 380 propensity-matched-cohort, the palbociclib group had significantly longer PFS (10 vs 5 months, P .0001) as well as OS (33 vs 24 months; P .022), compared to controls. We conclude that in this single center analysis of a large cohort of metastatic HR+ HER2- BC patients, palbociclib in combination with ET was associated with improved PFS in both first-line and second-line settings and OS in the second-line setting compared to ET alone cohort.

Background and Purpose: There is currently lack of recognized imaging criteria for prediction of treatment response to NAST in breast cancer patients. And early identification of treatment response to neoadjuvant systemic therapy (NAST) in Triple Negative Breast Cancer (TNBC) patients is important for appropriate treatment selection and response monitoring. A novel MRI sequence, Magnetic Resonance Image Compilation (MagIC) is capable of simultaneous quantitation of several tissue water properties including longitudinal (T1), transverse (T2) relaxation times, and proton density (PD). In this study we evaluated the ability of a radiomic model extracted from a novel MagIC sequence acquired early during NAST to predict pathologic complete response to NAST in TNBC. Materials and Methods: This IRB approved prospective ARTEMIS trial (NCT02276443) included 184 women (122 training dataset, 62 testing dataset) diagnosed with stage I-III TNBC. All patients were scanned with MagIC on a 3T MRI scanner at baseline (184 patients), and after 4 cycles (156 Patients) of NAST. T1, T2 and PD maps were generated from the source images using SyMRI (SyntheticMR, Linkoping, Sweden). Histopathology at surgery was used to determine pathologic complete response (pCR) which was defined as absence of the invasive cancer in the breast and axillary lymph nodes. 3D contouring of the tumors was performed using an in-house toolbox. 310 (10 first-order, 300 GLCM) textural features were extracted from each map, with total of 930 features/patient. Radiomic features were compared between pCR and non-pCR using Wilcoxon Rank Sum test and Fisher’s exact test. To build a multivariate, predictive model, logistic regression with elastic net regularization was performed for texture feature selection. The tuning parameter was optimized using 5-fold cross-validation based on the average area under curve (AUC) of each fold of a cross-validation using training data. Then the testing data were used to compare model’s performance by AUC. Results: Univariate analysis found 23 PD, 17 T1 and 10 T2 radiomic features at C4 time point to be able to predict pCR status with AUC >70% in both training and testing cohort. The top performing radiomic features were Entropy, Variance, Homogeneity and Energy (Tables1-2). Multivariate radiomics models from C4-PD, and C4-T1 maps showed best performance during both cross validation and independent testing. The radiomic signature of C4-T1 map that included 27features had best performance, with an AUC of 0.77, 0.70 (95% CI: 0.571-0.868) in training and testing cohort respectively. C4-PD map radiomic signature that included 6features was able to predict the pCR status with AUC of 0.73, 0.72 (95% CI: 0.571-0.868) in training and testing cohort respectively. Conclusion: Our data found that MagIC-based radiomics signature could potentially predict pathologic complete response in TNBC early during NAST. This data shows the potential application of MagIC radiomic model for improvement of response assessment in TNBC. Table 1.Best performing radiomic features from PD map after 4 cycles of NAST in TNBC patients.FeatureTraining CohortTraining CohortTraining CohortTesting CohortTesting CohortTesting CohortNAUC95% CINAUC95% CIP-valuePD-mapAngular Variance of Sum entropy1060.73820.6437-0.8328500.73240.5895-0.8752 Table 2.Best performing radiomic features from T1-T2 maps after 4 cycles of NAST in TNBC patients.FeatureTraining CohortTraining CohortTraining CohortTesting CohortTesting CohortTesting CohortNAUC95% CINAUC95% CIP-valueT1-mapAngular Variance of Sum entropy1060.76530.6762-0.8544500.70510.5524-0.8579 Citation Format: Nabil Elshafeey, Ken-Pin Hwang, Beatriz Elena Adrada, Rosalind Pitpitan Candelaria, Medine Boge, Rania M Mahmoud, Huiqin Chen, Jia Sun, Wei Yang, Aikaterini Kotrotsou, Benjamin C Musall, Jong Bum Son, Gary J Whitman, Jessica Leung, Huong Le-Petross, Lumarie Santiago, Deanna Lynn Lane, Marion Elizabeth Scoggins, David Allen Spak, Mary Saber Guirguis, Miral Mahesh Patel, Frances Perez, Abeer H Abdelhafez, Jason B White, Lei Huo, Elizabeth Ravenberg, Wei Peng, Alastair Thompson, Senthil Damodaran, Debu Tripathy, Stacey L Moulder, Clinton Yam, Mark David Pagel, Jingfei Ma, Gaiane Margishvili Rauch. Radiomics model based on magnetic resonance image compilation (MagIC) as early predictor of pathologic complete response to neoadjuvant systemic therapy in triple-negative breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr PD11-06.

Purpose: Several FGFR alterations have been found in breast cancer, however, their role as a therapeutic target in breast has been controversial. Futibatinib (TAS-120; Taiho) is a novel, selective pan-FGFR inhibitor which irreversibly binds to and inhibits FGFR1-4 at nanomolar concentrations. We sought to determine the efficacy of futibatinib in breast cancer models with differing FGFR alterations. Experimental Design: In vivo, antitumor efficacy was evaluated by tumor growth curves and event-free survival in a panel of patient-derived xenografts (PDXs) from breast cancer patients with different FGFR1-4 alterations. Genomic alterations in the PDXs were characterized by next generation sequencing. Correlation of FGFR gene expression in matched patient tumors and PDXs was analyzed by RNA sequencing. In vitro, FGFR2 Y375C mutant and FGFR2-BICC1 fusion expressing MCF10A cell lines were generated, and effect on cell proliferation, colony formation assay, and cell signaling was assessed with and without futibatinib. Frequency of FGFR mutations and FGFR2 amplification was compiled from internal and public databases. Results: Breast cancer PDXs varied in their expression of FGFR1-4. FGFR gene expression significantly correlated between matched patient tumors and PDXs derived from them, however, PDXs had higher levels of FGFR3 and FGFR4 expression compared to patient samples. Futibatinib inhibited tumor growth in three of 10 PDX models, with tumor stabilization in a FGFR2 amplified model and prolonged tumor regression (more than 110 days) in a PDX bearing a FGFR2 Y375C mutation. In vitro, expression of FGFR2 Y375C, as well as FGFR2-BICC fusion in normal-like MCF10A cells enhanced growth, colony formation ability and FGFR signaling. Cells expressing FGFR2 Y375C as well as FGFR2-BICC fusions were more sensitive to futibatinib. In the five breast cancer genomic series we analyzed, FGFR2 mutations and amplifications were found in 1.1%-2.6% and 1.4%-2.5%, respectively. Conclusions: Futibatinib had single agent activity of selected breast cancer PDX models. FGFR2 activating mutations and amplification may represent rare but promising therapeutic targets to FGFR inhibition. Citation Format: Turcin Saridogan, Argun Akcakanat, Ming Zhao, Kurt W. Evans, Erkan Yuca, Stephen Scott, Bryce P. Kirby, Xiaofeng Zheng, Senthil Damodaran, Funda Meric-Bernstam. Efficacy of futibatinib, an irreversible fibroblast growth factor receptor (FGFR) inhibitor, in breast cancer models with FGFR alterations [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 P5-08-12.

Background: Two PARP inhibitors are approved for germline BRCA1/2 mutant metastatic breast cancer (MBC), based on clinical trials demonstrating an improvement in patient outcomes and quality of life. However, germline BRCA1/2 mutations are identified in 5-10% of breast cancer, limiting their potential applicability. Our prior work demonstrated that somatic BRCA1/2 mutations can be detected in cell-free DNA (cfDNA) in a proportion of patients with MBC who are not germline BRCA1/2 carriers, and that a PARP inhibitor caused growth inhibition in a circulating tumor cell line generated from a patient with MBC and a pathogenic somatic BRCA1 mutation (Vidula, Dubash, CCR, 2020). Thus, we hypothesize that a PARP inhibitor may have efficacy in somatic BRCA1/2 mutant MBC identified by cfDNA. Trial Design: This phase II investigator initiated open label clinical trial is enrolling 30 patients who have pathogenic somatic BRCA1/2 mutations found in cfDNA. Patients must not be known germline BRCA1/2 carriers. Patients receive treatment with the PARP inhibitor, talazoparib, until disease progression. Serial imaging (CT chest, abdomen, pelvis, and bone scan) occurs every 3 months, and cfDNA is collected monthly to evaluate changes in the genomic environment. Patients will also have blood collected at baseline for the Cancer Risk B assay (CR-B), a novel flow variant assay to assess double strand break repair mutations in circulating blood cells (Syeda, Genetics, 2017). Eligibility criteria: Patients with MBC (TNBC with ≥ 1 prior chemotherapy or HR+/HER2- with ≥ 1 prior hormone therapy or ineligible for hormone therapy) with a somatic BRCA1/2 mutation identified in cfDNA (established pathogenic variant) are being enrolled. Patients should not be known germline BRCA1/2 carriers (genetic testing is not required but can be obtained per physician discretion) and may not have previously received a PARP inhibitor. There is no limit on the number of prior therapies, and a prior platinum chemotherapy is allowed in the absence of disease progression on the platinum. Patients must have adequate performance status and organ function. Specific Aims: The primary endpoint is progression-free survival (PFS) using RECIST 1.1. Secondary endpoints include objective response rate and toxicity (NCI CTCAE v 5.0). Exploratory objectives include evaluating serial changes in BRCA1/2 mutant allelic frequency in cfDNA, evaluating the impact of BRCA1/2 reversion mutations, comparing pre- and post-treatment cfDNA results to identify markers of resistance, evaluating the CR-B assay positivity rate, and ultimately correlating these analyses with treatment response. Statistical Methods: A two-stage design with 80% power to demonstrate that talazoparib is associated with “success” (PFS > 12 weeks) in ≥53% patients (4% alpha) is being used. Accrual: This study (NCT03990896) is currently open at Massachusetts General Hospital, where 4 patients are completing screening for enrollment. This study will be activated soon at the University of California San Francisco, MD Anderson, Mayo Clinic Rochester and Jacksonville, Northwestern, and Emory (7 academic centers). Funding: Support for this study is provided by a Pfizer ASPIRE award and Conquer Cancer Foundation of ASCO–Breast Cancer Research Foundation- Career Development Award. Contact information: Neelima Vidula, MD, Massachusetts General Hospital, nvidula@mgh.harvard.edu Citation Format: Neelima Vidula, Erica Blouch, Erin Basile, Nathan Royce Ruffle-Deignan, Nora Horick, Senthil Damodaran, Alvaro Moreno Aspitia, Manali Bhave, Ami Shah, Minetta C. Liu, Joseph Sparano, Harry Ostrer, Hope Rugo, Leif W. Ellisen, Aditya Bardia. Phase II study of a PARP inhibitor in metastatic breast cancer with somaticBRCA1/2mutations identified by cell-free DNA: Genotyping based clinical trial [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT2-24-03.

PURPOSE: Cyclin-dependent kinase 4/6 inhibitor (CDKi) therapy combined with endocrinetherapy is considered standard of care for patients with advanced hormone receptor (HR)-positive, HER2-negative breast cancer (BC). The Breast Medical Oncology Database at MDAnderson Cancer Center (MDACC) was analyzed to assess effectiveness of CDKi+palbociclib. PATIENTS AND METHODS: From a total of 5402 advanced HR+ HER2- BC patients referred toMDACC between 1997 and 2020, we identified eligible patients who received palbociclib incombination with first- (n=778) and second-line (n=410) endocrine therapy. We furtheridentified “control” patients who received endocrine therapy alone in the first- (n=2452) andsecond-line (n=1183) setting. We conducted a propensity score matching analysis to balancethe baseline demographic and clinical characteristics between the palbociclib treated andcontrol cohorts to assess the effect of palbociclib treatment on progression-free survival (PFS)and overall survival (OS). Stratified log-rank test was used to assess the effect of palbociclib inthe matched cohorts. RESULTS: For the propensity-matched cohort in the first-line setting (n=708), the palbociclibgroup had significantly longer median PFS (17.4 vs. 11.1 months; p Citation Format: Akshara Singareeka Raghavendra, Min Jin Ha, Nicole M. Kettner, Senthil Damodaran, Rachel Layman, Kelly K Hunt, Yu Shen, Debu Tripathy, Khandan Keyomarsi. Palbociclib plus endocrine therapy significantly enhances overall survival of HR+/HER2- metastatic breast cancer patients compared to endocrine therapy alone - A large institutional study [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-19-01.

Background: Datopotamab deruxtecan (Dato-DXd) is an antibody-drug conjugate consisting of a humanized anti-TROP2 IgG1 monoclonal antibody conjugated to a potent topoisomerase I inhibitor payload via a stable tetrapeptide-based cleavable linker. Preliminary results from the phase 1 TROPION-PanTumor01 study demonstrate that Dato-DXd has encouraging antitumor activity and a manageable safety profile in patients with non-small cell lung cancer (NSCLC) (Meric-Bernstam, ASCO 2021) and those with triple-negative breast cancer (TNBC) (Bardia, ESMO BC 2021). Updated results from the TNBC cohort are presented here. Methods: TROPION-PanTumor01 (NCT03401385) is a phase 1, multi-center, open-label, 2-part study evaluating Dato-DXd in previously treated patients with solid tumors. Based on the dose-escalation results in patients with NSCLC, Dato-DXd 6 mg/kg intravenously every 3 weeks is being evaluated in patients with advanced/metastatic TNBC and HR+/HER2− breast cancer who relapsed/progressed on standard therapies. Two patients with TNBC received Dato-DXd 8 mg/kg prior to selection of 6 mg/kg for dose expansion. Safety and efficacy were assessed, including objective response rate (ORR) per RECIST version 1.1 by blinded independent central review (BICR). Results: As of the April 6, 2021, data cutoff, 43 patients with TNBC had received ≥1 dose of Dato-DXd, with 27 patients (63%) continuing and 16 patients (37%) discontinuing treatment all due to disease progression. The median age was 53 years (range, 32-82 years). Forty-one patients (95%) had received ≥2 prior lines of therapy; 19 patients (44%) had received prior immunotherapy and 7 (16%) had received prior sacituzumab govitecan. The median duration of treatment was 2.8 months (range, 0.7-6.9 months). The median follow-up was 3.9 months (range, 0.3-9.2 months). Among 38 patients evaluable for response, the ORR by BICR was 39% (15 partial responses [PR]), with 12 confirmed and 3 pending confirmation. The disease control rate was 84% (32/38). The median time to response was 1.35 months (1.2-3.2 months) for the 12 confirmed PRs. All-cause treatment-emergent adverse events (TEAEs; any grade, grade ≥3) were observed in 95% and 35% of patients, respectively; 2 events were grade 4 and 0 grade 5. The most common TEAEs (any grade [≥30%], grade ≥3) included nausea (58%, 0%), stomatitis (53%, 9%), alopecia (35%, N/A), vomiting (35%, 2%), and fatigue (33%, 7%). One patient had grade 3 decreased neutrophil count; no cases of grade ≥3 diarrhea were observed. No cases of treatment-related interstitial lung disease as adjudicated by an independent committee were reported. Serious TEAEs were observed in 5 patients (12%); no TEAEs were associated with death. Dose reductions occurred in 9 patients due to stomatitis, fatigue, mucosal inflammation, dry eye, retinal exudates, and blurred vision (multiple counts per TEAE). Three patients had dose interruptions due to stomatitis, mucosal inflammation, bronchitis, and musculoskeletal chest pain. No patients discontinued treatment due to adverse events. Conclusions: Preliminary results showed that Dato-DXd demonstrates promising antitumor activity with a manageable safety profile in patients with previously treated advanced/metastatic TNBC; confirmatory studies in patients with breast cancer are warranted. Citation Format: Ian Krop, Dejan Juric, Toshio Shimizu, Anthony Tolcher, Alexander Spira, Toru Mukohara, Aaron E. Lisberg, Takahiro Kogawa, Kyriakos P. Papadopoulos, Erika Hamilton, Senthil Damodaran, Jonathan Greenberg, Wen Gu, Fumiaki Kobayashi, Ferdinand Guevara, Takahiro Jikoh, Yui Kawasaki, Funda Meric-Bernstam, Aditya Bardia. Datopotamab deruxtecan in advanced/metastatic HER2- breast cancer: Results from the phase 1 TROPION-PanTumor01 study [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 GS1-05.

Background: FGFR gene amplifications are found in 18% of breast cancers (BCs), with FGFR1 amplifications occurring in ≈10% of cases, predominantly in hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2−) MBCs. FGFR1 amplifications are associated with resistance to endocrine therapy, and in preclinical experiments, FGFR pathway inhibition has been shown to overcome resistance to hormone therapy in BC harboring FGFR1 amplifications. Futibatinib, a highly selective, irreversible FGFR1-4 inhibitor, has shown preclinical activity in BC xenograft models harboring FGFR1/2 amplifications. In a phase 1 study, futibatinib showed promising clinical activity and tolerability across tumor types, including MBC, harboring various FGFR aberrations. A multicohort phase 2 trial (FOENIX-MBC2; NCT04024436) was designed to evaluate futibatinib alone (cohorts 1-3) or in combination with fulvestrant (cohort 4) in patients with MBC harboring FGFR2 or FGFR1 amplifications, respectively. Here, we report preliminary safety data from cohort 4 of FOENIX-MBC2, including data from a safety lead-in. Methods: Cohort 4 of FOENIX-MBC2 enrolled adult patients with HR+ HER2− MBC harboring high levels of FGFR1 amplification (FGFR1:CEN8 ratio ≥5 or FGFR1 copy number ≥10 signals per cell), Eastern Cooperative Oncology Group performance status 0-1, and adequate organ function. Patients were fulvestrant naive and had previously received 1-2 endocrine-containing therapies, ≤1 chemotherapy regimen, and a CDK4/6 inhibitor (if eligible). Cohort 4 began with a safety lead-in to assess dose-limiting toxicities (DLTs) during the first treatment cycle. Patients received oral futibatinib 20 mg once daily continuously, and intramuscular fulvestrant 500 mg was administered on days 1 and 15 of cycle 1 and day 1 of every subsequent 28-day cycle. Patients were treated until disease progression, unacceptable toxicity, or another discontinuation criterion was met. Results: As of data cutoff (March 31, 2021), cohort 4 had enrolled 8 female patients with HR+ HER2− MBC harboring high-level FGFR1 amplification. The median age was 55.5 years (range: 31-62 years), and all patients had received ≥2 prior therapies for advanced/metastatic BC. The median duration of treatment was 8.0 weeks (range: 3.0-32.7 weeks); 3 of 8 patients (38%) were continuing treatment at time of data cutoff. All patients experienced treatment-related adverse events (TRAEs; grade ≥3: 25%). The most common TRAE was hyperphosphatemia (88%), followed by constipation (62%), transaminase elevation (50%), dry mouth (38%), and alopecia (38%). Among these TRAEs, grade ≥3 events were only reported for hyperphosphatemia (12%), and no serious adverse events were reported. In this cohort, TRAEs led to dose reductions in 4 patients, dosing interruptions in 3 patients, and treatment discontinuation in 1 patient; no patients died due to TRAEs. DLTs were evaluated in 5 patients following 1 treatment cycle (1 patient was enrolled after data cutoff, and 4 of 9 patients were not evaluable for DLTs); DLTs were not experienced by any of the 5 evaluable patients. Conclusions: Based on these preliminary safety results, the combination of futibatinib and fulvestrant appears to be safe and tolerable in patients with HR+ HER− MBC harboring high-level FGFR1 amplification. The safety profile was consistent with the individual profiles of both drugs, and the treatment combination did not appear to result in synergistic toxicity. As no DLTs were observed in 5 evaluable patients, the recommended futibatinib dose in combination with fulvestrant is 20 mg once daily. Efficacy will be evaluated in the complete 28-patient post-lead-in cohort, in which enrollment is ongoing. Citation Format: Senthil Damodaran, Nisha Unni, Karthik V. Giridhar, Brooke Daniel, Sacha Howell, Luis Costa, Marta Ferreira, Masashi Shimura, Gareth Tomlinson, Maciej Gil, Nicholas Turner. Futibatinib in combination with fulvestrant in patients with metastatic breast cancer (MBC) harboring high-level FGFR1 amplification: Preliminary data from a phase 2 study [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-18-35.

The role of the fibroblast growth factor receptor (FGFR) gene alterations as therapeutic targets in breast cancer have not been well characterized. Futibatinib (TAS-120; Taiho) is a novel pan-FGFR inhibitor. We sought to determine the efficacy of futibatinib in breast cancer models with FGFR alterations. Nine breast cancer patient–derived xenografts (PDXs) with a variety of FGFR1-4 alterations and expression levels were treated with futibatinib. FGFR gene expression between patient tumors and matching PDXs was significantly correlated. Futibatinib inhibited tumor growth in 3 of 9 PDXs, with tumor stabilization in an FGFR2-amplified model and prolonged regression in an FGFR2 Y375C mutant/amplified model. FGFR2 overexpression and, to a greater extent, FGFR2 Y375C expression in MCF10A cells enhanced cell growth and sensitivity to futibatinib. Per institutional and public databases, FGFR2 mutations and amplifications had a population frequency of 1.1–2.6% and 1.5–2.5%, respectively. FGFR2 alterations in breast cancer may represent infrequent but highly promising targets for futibatinib.

Purpose: Increasing tumor-infiltrating lymphocytes (TIL) is associated with higher rates of pathologic complete response (pCR) to neoadjuvant therapy (NAT) in patients with triple-negative breast cancer (TNBC). However, the presence of TILs does not consistently predict pCR, therefore, the current study was undertaken to more fully characterize the immune cell response and its association with pCR. Experimental Design: We obtained pretreatment core-needle biopsies from 105 patients with stage I–III TNBC enrolled in ARTEMIS (NCT02276443) who received NAT from Oct 22, 2015 through July 24, 2018. The tumor-immune microenvironment was comprehensively profiled by performing T-cell receptor (TCR) sequencing, programmed death-ligand 1 (PD-L1) IHC, multiplex immunofluorescence, and RNA sequencing on pretreatment tumor samples. The primary endpoint was pathologic response to NAT. Results: The pCR rate was 40% (42/105). Higher TCR clonality (median = 0.2 vs. 0.1, P = 0.03), PD-L1 positivity (OR: 2.91, P = 0.020), higher CD3+:CD68+ ratio (median = 14.70 vs. 8.20, P = 0.0128), and closer spatial proximity of T cells to tumor cells (median = 19.26 vs. 21.94 μm, P = 0.0169) were associated with pCR. In a multivariable model, closer spatial proximity of T cells to tumor cells and PD-L1 expression enhanced prediction of pCR when considered in conjunction with clinical stage. Conclusions: In patients receiving NAT for TNBC, deep immune profiling through detailed phenotypic characterization and spatial analysis can improve prediction of pCR in patients receiving NAT for TNBC when considered with traditional clinical parameters.

BACKGROUND: Intra-tumoral Clostridium novyi-NT (non-toxic) is an attenuated strain of C. novyi lacking alpha toxin replication within hypoxic tumor regions, causing tumor cell lysis and inflammation. Immunotherapy (IO) augments anticancer activity with intratumoral agents in prior preclinical and clinical studies. This phase 1b dose escalation study assessed safety and potential synergistic effects of pembrolizumab and C. novyi-NT in advanced solid tumors. METHODS: We enrolled patients with percutaneous injectable, solid tumors to receive single intratumoral injection of C. novyi-NT administered on Day 8 across 4 dose cohorts (3 × 10^4 to 100 × 10^4 spores, 3+3 design) with pembrolizumab 200mg IV Q3weekly starting on Day 0 up to 24 months. Primary objectives: Safety, tolerability and maximum tolerated dose (MTD) of combination. Secondary objectives: anti-tumor activity of combination in the injected tumor lesion and overall response by iRECIST 1.1. RESULTS: At data cutoff on October 24, 2022, 16 patients were enrolled and evaluable for toxicity and efficacy. It was well tolerated across all cohorts without dose limiting toxicities with median number of 5 cycles administered (1-34). 10 patients (63%) experienced progression; 1 withdrew consent; 1 completed therapy; 1 came off trial due to toxicity (immune related dermatitis) and 3 patients remain on trial. Median age was 62.5 years (40-71) while all patients (100%) had performance status of 1. 8 (50%) received prior IO and 7 (44%) had > 4 lines of prior therapies. Confirmed overall objective response rate (ORR) was 25% in 4 patients [non-keratinizing undifferentiated nasopharyngeal squamous carcinoma (NPC), human papilloma virus positive squamous cell carcinoma of base of tongue, vulvar melanoma and chordoma] with 3 partial responses (PR) and 1 complete response (CR). Among responders, median duration of response was 8.18 months and 1/4 (25%) had prior IO. NPC patient completed 24 months on trial to completion with best response at PR (-87%) while vulvar melanoma patient remains on trial with best response at CR (-100%). Median injected tumor size was 2.65cm (1-11) with confirmed ORR in injected lesions at 19% with 2 PRs and 1 CR. Most prevalent grade 1 and 2 adverse events were injection site reaction (25%), pyrexia (19%), pruritus (13%), leukopenia (13%) and anemia (13%). No grade 3 or 4 treatment related adverse events noted. Signs and symptoms of C. novyi-NT germination (infection) including fever, injection site pain, erythema, swelling, tenderness, and in some cases, ulceration, spontaneous drainage, tissue sloughing, bleeding, and malodor were observed in 5 patients. CONCLUSIONS: Intratumoral C. novyi-NT with pembrolizumab demonstrates clinical activity with favorable tolerability in patients regardless of tumor histology. This study is ongoing to define the recommended phase 2 dose (NCT03435952). Citation Format: Blessie Elizabeth Nelson, Filip Janku, Siqing Fu, Ecaterina I. Dumbrava, David S. Hong, Daniel Karp, Aung Naing, Jordi Rodon, Apostolia Tsimberidou, Rodabe N. Amaria, Anthony Conley, Senthil Damodaran, Kanwal P. Raghav, Brent L. Kreider, David Tung, Mary Varterasian, Khashayarsha Khazaie, Sarina Piha-Paul. Phase Ib Study of Pembrolizumab in Combination with Intratumoral Injection of Clostridium novyi-NT in Patients with Advanced Solid Tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT107.

Background: In the metastatic setting, low HER2 expression is associated with clinical benefit from trastuzumab deruxtecan, a HER2-targeting antibody drug conjugates. However, little is known about the biological significance of low HER2 expression in patients with early stage triple-negative breast cancer (TNBC) receiving neoadjuvant therapy (NAT). Methods: Out of 595 patients with stage I-III TNBC enrolled on the prospective ARTEMIS trial (NCT02276443) from 2015-2021, we identified 367 patients with available HER2 immunohistochemistry (IHC) results on pre-NAT tumor tissue (HER2-zero: n=218; HER2-low [IHC 1+, 2+]: n=149). All patients were treated with anthracycline-based NAT. In cases where sufficient pre-NAT tumor tissue were available, additional IHC and/or RNAseq were performed. Differential gene expression (DGE) and pathway analysis were performed using DEseq2. Gene set enrichment analysis (GSEA) was performed using the Hallmark gene sets. Deconvolution analyses were performed using CIBERSORT. We controlled for multiple hypothesis using a false discovery rate (FDR) threshold with the Benjamini-Hochberg method, accepting as significant genes with at least a 2-fold change and < 5% FDR. Results: Table 1 summarizes baseline clinicopathological features of the 367 patients. Compared to HER2-zero tumors, HER2-low tumors were less likely of metaplastic histology (p=0.001), associated with lower Ki67 (p=0.017) and were more likely to be androgen receptor (AR)-positive (p=0.01). There were no significant differences in tumor-infiltrating lymphocytes (TILs) infiltration and PD-L1 expression between HER2-zero and HER2-low tumors. Among the 226 patients with sufficient pre-NAT tissue for RNAseq, DGE analyses demonstrated upregulation of genes involved in fatty acid metabolism (ACSM1) and steroid hormone metabolism (DHRS2, UGT2B28) in HER2-low tumors compared with HER2-zero tumors. Deconvolution analyses revealed no significant differences between predicted proportions of immune cell subpopulations between HER2-low and HER2-zero tumors. Although rates of pCR were not significantly different between patients with HER2-zero (46%) and HER2-low tumors (40%) (p=0.34), non-pCR in patients with HER2-low tumors was associated with increased expression of EREG, which encodes an EGFR ligand, while non-pCR in patients with HER2-zero tumors was associated with downregulation in genes involved in immune response pathways. GSEA further identified the Hallmark allograft rejection (FDR q=0.001), interferon gamma response (FDR q=0.002), and interferon alpha response pathways (FDR q=0.007) as the 3 most significantly downregulated pathways in HER2-zero tumors from patients experiencing a non-pCR relative to HER2-zero tumors from patients experiencing a pCR. Conclusion: In early stage TNBC, low HER2 expression is associated with increased AR expression and upregulation of genes associated with fatty acid and steroid hormone metabolism. Gene expression analyses suggest that drivers of resistance to NAT differ between HER2-low and HER2-zero tumors. Biological differences between HER2-zero and HER2-low tumors exist and may influence future personalized treatment for patients with early stage TNBC. Citation Format: Clinton Yam, Ziyi Li, Anil Korkut, Wencai Ma, Elisabeth Kong, Holly A. Hill, Hussein Abbas, Sausan Abouharb, Beatriz Adrada, Banu K. Arun, Carlos H. Barcenas, Ajit Bisen, Daniel Booser, Aman Buzdar, Rosalind Candelaria, Junjie Chen, Alyson Clayborn, Senthil Damodaran, Qingqing Ding, Haven Garber, Gabriel N. Hortobagyi, Kelly K. Hunt, Nuhad K. Ibrahim, Adaeze Iheme, Meghan S. Karuturi, Kimberly Koenig, Rachel M. Layman, Jangsoon Lee, Jennifer K. Litton, Melissa Mitchell, Giancarlo Moscol, Jason Mouabbi, Rashmi K. Murthy, Oluchi Oke, Paula Pohlmann, David Ramirez, Elizabeth Ravenberg, Sadia Saleem, Mediget Teshome, Vicente Valero, Jason White, Madison Williams, Wendy Woodward, Chasity Yajima, Naoto T. Ueno, Ken Chen, Gaiane Rauch, Lei Huo, Debu Tripathy. HER2-01 Clinical and Molecular Characteristics of HER2-low/zero Early Stage Triple-Negative Breast Cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr HER2-01.

Background: Metastatic TNBC is an aggressive breast cancer subtype with poor prognosis and limited systemic therapy options. While pembrolizumab in combination with chemotherapy is approved for PD-L1 positive TNBC, limited immunotherapy options exist for patients with progressive and/or PD-L1 negative disease. TGFβ released by cancer cells and stromal fibroblasts attenuates the intrinsic antitumor potential of immune cells within the tumor microenvironment mediating resistance to immunotherapy. Consequently, inhibition of TGFβ signaling could potentially enhance antitumor responses to anti-PD-L1/PD-1 therapies. Bintrafusp alfa is a bifunctional fusion protein composed of the extracellular domain of TGF-β receptor II (a TGF-β “trap”) fused to a human IgG1 monoclonal antibody blocking programmed cell death ligand 1. Preclinical studies have shown that eribulin downregulates TGFβ by phosphorylation of Smad proteins. Therefore, combining eribulin with bintrafusp alfa may have a synergistic effect. This study evaluated the combination of bintrafusp alfa with eribulin in patients with metastatic TNBC. Methods: This is a phase 1b, open label, single center study evaluating bintrafusp alfa in combination with eribulin in patients with metastatic TNBC who had relapsed/progressed on prior therapies. Patients with ER/PR ≤10% with measurable disease were enrolled. Patients who received prior anti-PD-1/PD-L1 therapies in the metastatic setting were excluded. Patients received bintrafusp alfa 1200 mg intravenously every 2 weeks in combination with eribulin (1.4 mg/m2 (dose level 1), 1.1 mg/m2, or 0.7 mg/m2) on days 1, 8, 22, 29 on every 6-week cycle. Primary objectives were to determine the recommended phase II dose (RP2D) as well as to evaluate the safety and tolerability of eribulin in combination with the fixed dose of bintrafusp alfa. Secondary objective was to determine the overall response rate (ORR) according to RECIST 1.1. Bayesian optimal interval (BOIN) design was employed to identify the RP2D. Toxicities assessed using CTCAE v4.03. Tumor assessments were performed every 6 weeks. Results: A total of 25 patients were enrolled on the study. Twenty-one patients were evaluable (3 screen failures, 1 received only one dose of study treatment). Median age 59 (range 27-85). Median number of prior therapies 2 (range 0-8). The most common reason for protocol discontinuation was disease progression (n = 15, 71%). Four patients experienced dose limiting toxicities (DLTs); 3 with decreased neutrophil count and 1 with increased aspartate aminotransferase. Five patients (24%) experienced grade 4 toxicities (increased aspartate aminotransferase, hypokalemia, hypophosphatemia, neutropenia). Nine patients (43%) experienced grade 3 toxicities. Three patients (14%) discontinued study due to toxicity. Total of 2 deaths were observed, none related to treatment. Most common toxicities (any grade) include anemia (n = 13 patients), elevated aspartate aminotransferase (11), neutropenia (n = 10), elevated aminotransferase (9), headache (n = 9), hypokalemia (n = 8), hyperglycemia (n = 8), leukopenia (n = 8), and fatigue (n = 8). RP2D was eribulin 1.1 mg/m2 with bintrafusp alfa 1200 mg. Six patients had PR (28.6%), 2 had SD (9.5%) and 12 had PD (57.1%) as the best response. One patient withdrew before response evaluation. Median PFS was 1.7 months (95% CI: (1.2, 5.9) and median OS was 11.1 months (95%CI: (5.2, 15.7). Conclusions: The combination of bintrafusp alfa with eribulin has manageable safety profile with meaningful clinical activity in patients with TNBC. Further studies evaluating TGF inhibitors in breast cancer are warranted. Citation Format: Senthil Damodaran, Diane Liu, Jill Schwartz, Vicente Valero, David Ramirez, Sadia Saleem, Naoto T. Ueno, Nuhad K. Ibrahim, Meghan S. Karuturi, Rashmi K. Murthy, Stacy Moulder, Jennifer K. Litton. A phase Ib trial of bintrafusp alfa and eribulin in patients with metastatic triple negative breast cancer (TNBC) [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-02-03.

Introduction: Use of long-term endocrine therapy (ET) for ER+ breast cancer often leads to acquired ESR1 mutations (mutESR1), causing endocrine resistance, tumor progression, and poor prognosis. An unmet clinical need exists for treating ER+ mBC patients with mutESR1, particularly after progression on CDK4/6 inhibitors (CDK4/6i). ELAINE 2 is an open-label, phase 2, multicenter trial evaluating safety and efficacy of lasofoxifene (LAS [selective estrogen receptor modulator]) plus abemaciclib (Abema [CDK4/6i], provided by Eli Lilly) in patients with ER+/HER2- and mutESR1 mBC who progressed after prior ET. Preliminary data with LAS plus Abema showed median progression-free survival of 55.7 wks, objective response rate of 50%, and 24-wk clinical benefit (CB) rate of 69%, with an acceptable safety and tolerability profile. Here, we report ESR1 ctDNA mutant allele frequency (MAF) and correlations of ESR1 MAF changes with CB. Methods: ELAINE 2 patients with detectable ctDNA mutESR1 at baseline (BL) were analyzed. Oral LAS 5 mg/day and Abema 150 mg BID were taken until disease progression, death, unacceptable toxicity, or withdrawal from the study. ctDNA was assessed by the Sysmex-Inostics SafeSeq assay—which detects mutESR1 at low allele fractions—at BL, every 4 wks, and end of treatment. MAF changes from BL to wk 4 were characterized as decreased (decrease in ESR1 MAF or none detected [ND]), increased (increase in MAF), or equivocal (in polyclonal patients [>1 mutESR1] with some MAF increasing and decreasing trends). Correlations of MAF change at 4 wks with CB at 24 wks were explored. Results: 29 patients (median of 2 prior metastatic therapies: 97% CDK4/6i, 79% fulvestrant, 48% chemotherapy) had BL mutESR1 of Y537S (66%), D538G (45%), Y537N (28%), and other less frequently detected mutations; 14 (48.3%) patients were polyclonal. 26 of 29 patients had evaluable BL and wk-4 ctDNA results: 21 patients had decreased MAF (81% [54% with ND]), 3 (12%) had increased, and 2 (8%) had equivocal ESR1 MAF changes (Table). CB at 24 wks was seen in 17 patients with a decrease, 2 with an increase, and 1 with equivocal MAF change. A sensitivity of 89.5% and specificity of 20% were calculated for predicting CB based on direction of ESR1 MAF change. The positive predictive value (PPV) for CB with decreased MAF was 81% and the negative predictive value (NPV) for an increased MAF was 33%. Of the 14 (54%) patients with ND ESR1 MAF, 13 had CB resulting in 87% sensitivity, 50% specificity, 93% PPV, and 33% NPV. Conclusion: In ELAINE 2, 81% of patients had decrease/cleared (ND) mutESR1 after 4 wks of LAS plus Abema, which correlated with clinical benefit. All mutESR1 detected appear targeted with this therapy. High sensitivity and favorable PPV were observed in patients with decreased MAF, and even more so in those with ND MAF; however, increased MAF was less specific and not as predictive of treatment failure. Our results indicate that ESR1 liquid biopsy evaluation may be an adequate non-invasive surrogate marker for monitoring patients on treatment. Further study in a larger population of women with endocrine-resistant mBC and acquired mutESR1 is warranted to explore this potential for monitoring treatment response or resistance to this novel LAS-Abema combination. Table. Change from baseline to week 4 in ESR1 MAF and clinical benefit at 24 weeks. CI, confidence interval; MAF, mutant allele fraction; ND, none detected; NPV, negative predictive value; PPV, positive predictive value. *Sensitivity and specificity analyses do not include equivocal results. Citation Format: Senthil Damodaran, Halle Moore, Ciara C. O’Sullivan, Paul V. Plourde, Gary Riordan, Hillary S. Sloane, Debu Tripathy, Dominic Carroll, David J Portman. Estrogen receptor 1 (ESR1) mutations in circulating tumor DNA (ctDNA) from patients with ER+/HER2- metastatic breast cancer (mBC) treated with lasofoxifene plus abemaciclib in the ELAINE 2 study [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-05-02.

Nearly two-thirds of breast cancers overexpress estrogen receptors, and endocrine therapy is considered the backbone of systemic therapy both in early and advanced settings. While this is now widely recognized in clinical practice, this is the culmination of outstanding contribution of many investigators and patients. Indubitably, estrogen receptor targeting has had the most impact among targeted therapies and has significantly affected patient survival. In this commentary, we revisit a landmark article published in Cancer Research in 1977 by Knight and colleagues, which laid the groundwork for the use of estrogen receptors in prognostication and adjuvant treatment selection, as well as some of the key breakthroughs in estrogen receptor biology that span more than a century. See related article by Knight and colleagues, Cancer Res 1977;37:4669–71

High-throughput methods for single cell copy number sequencing have enabled the profiling of thousands of cells in parallel, yet there remains a significant bottleneck for data analysis. Here we present CopyKit, a comprehensive set of computational methods for the pre-processing and analysis of single cell copy number data to resolve clonal substructure and reconstruct genetic lineages in tumors. We performed single cell DNA sequencing of 2977 cells from multiple spatial regions in two liver metastasis and 7365 cells from three primary tumors with matched metastatic tissues. In the liver metastases, CopyKit resolved clonal substructure in different spatial regions, which revealed both clonal intermixing and spatial segregation in the tumor mass. In the matched metastatic colorectal and breast cancers, CopyKit resolved metastatic lineages and identified subclones and genomic events that were associated with metastases. These applications show that CopyKit is comprehensive tool for resolving copy number substructure in tumors.

Folate receptor alpha (FRα) has been reported to be expressed in up to 80% of triple-negative breast cancers (TNBC) with limited expression in normal tissues, making it a promising therapeutic target. Mirvetuximab soravtansine (mirvetuximab-s) is an antibody drug conjugate which has shown promise in the treatment of FRα-positive solid tumors in early phase clinical trials. Herein, are the results of the first prospective phase II trial evaluating mirvetuximab-s in metastatic TNBC. Patients with advanced, FRα-positive TNBC were enrolled on this study. Mirvetuximab-s was administered at a dose of 6.0 mg/kg every 3 weeks. 96 patients with advanced TNBC consented for screening. FRα staining was performed on tumor tissue obtained from 80 patients. The rate of FRα positivity by immunohistochemistry was 10.0% (8/80). Two patients were treated on study, with best overall responses of stable disease in one and progressive disease in the other. Adverse events were consistent with earlier studies. The study was terminated early due to the low rate of FRα positivity in the screened patient population and lack of disease response in the two patients treated. The observed rate of FRα positivity was considerably lower than previously reported and none of the patients had a partial or complete response. Treatment with mirvetuximab-s should only be further explored in TNBC if an alternate biomarker strategy is developed for patient selection on the basis of additional preclinical data.

Mammary Paget disease (MPD) comprises 1.45% all male breast cancers, compared with only 0.68% of all female breast cancers. Patients usually present in the fifth and sixth decades of life with ulceration, eczematous changes, discharge, bleeding, itching, and induration of the nipple and areola. Typically, there is a delay in definitive diagnosis and treatment from the onset of symptoms because most patients are initially treated for a rash. At the time of diagnosis, about half of the patients may have palpable breast mass, positive lymph nodes, or both. In this article, we present 2 cases of male MPD representing the extremes of clinical, radiologic, and histopathologic spectrum of the disease. One patient presented with a rash of the nipple of several months duration without an underlying lesion, whereas the other presented with sensitivity and pain of the nipple for 1 year and an underlying mass. Biopsies were diagnostic of MPD in both cases, and definitive surgery revealed an underlying ductal carcinoma in situ in the first case and an invasive ductal carcinoma in the second, highlighting the importance of early biopsy to initiate appropriate management.

One of the important applications of genetic testing is genetic testing of the tumor to identify non-inherited somatic mutations. The advent of high-throughput genomic and proteomic techniques has enabled characterization of genomic alterations and accelerated development of novel matching therapies for cancer. Consequently, mutational status has increasingly defined treatment selection for patients with solid tumors. The effectiveness of targeted therapy depends on matching with the right target; targets that are differentially expressed in tumor cells and provide growth and survival advantage. Currently, multiple targeted therapies have been approved by the Food and Drug Administration (FDA) for treatment of solid tumors including breast, lung, and melanoma, while many others are being evaluated in clinical trials. In addition to identifying actionable genomic alterations of interest, tumor genome sequencing also has the potential to detect germline mutations that has clinical implications for both the patient and their family. While targeted therapies have transformed our approach to cancer care in solid tumor patients within the past decade, lack of sustained responses and emergence of acquired resistance limit their clinical activity. In this article, we discuss tumor genome sequencing in breast cancers and their clinical implication.

Introduction High levels of TIL at baseline are associated with higher pCR rates and better overall survival in TNBC. Recent studies have also indicated that higher TIL in post-NACT residual disease in TNBC are an important independent predictor of improved survival. We evaluated the role of mid-treatment (post-AC; Adriamycin/Cyclophosphamide) TIL in predicting pCR rates in early-stage TNBC. Methods Of 242 patients with stage I-III TNBC enrolled in the ARTEMIS trial (NCT02276443), 156 patients had pre-AC TIL and pCR status available for this analysis. Both pre-and post-AC TIL counts were available in 29 patients. Post-AC TIL counts for the remaining patients were imputed using linear regression with age, race, stage III, vimentin >50% and post-AC tumor volume reduction. Using these imputed TIL counts we evaluated the association of post-AC TIL with pCR. We also evaluated the change in TIL before and after treatment with AC. Results At baseline the median TIL count was 10% (n=156). In the post-AC samples, the median TIL count was 5%. Using imputed TIL counts, we did not conclude that post-AC TIL was associated with pCR (p= 0.28). Using a cut-point of 15% TIL, our analysis showed that baseline TIL is more strongly correlated with pCR than post-AC TIL (Table 1). In our univariable logistic regression, both baseline TIL and the difference in TIL pre-and post- treatment were significantly associated with pCR (p= 0.0015 and p=0.0068, respectively), however in the multivariable analysis only baseline TIL was significant. Our analysis did show that a decrease in TIL from pre- to post-treatment was significantly associated with pCR (p=0.022). However, this measure was not significant in our logistic regression model when pre-TIL was also included. Conclusion Higher pre-treatment TIL correlated more strongly with pCR rate when compared to post-AC TIL. Pre-treatment high TIL was associated with pCR regardless of changes in TIL pre and post treatment. Table 1. Changes in TIL before and after treatmentBaseline TILPost-AC TILN#pCR (%)LowLow6217 (27%)LowHigh4012 (30%)HighLow2513 (52%)HighHigh2916 (55%)TIL; Low: 15 Citation Format: Nour Abuhadra, Kenneth Hess, Jennifer Litton, Gaiane Rauch, Alastair Thompson, Bora Lim, Beatriz Adrada, Elizabeth Mittendorf, Senthil Damodaran, Rosalind Candelaria, Banu Arun, Wei Tse Yang, Naoto Ueno, Lumarie Santiago, Rashmi Murthy, Nuhad Ibrahim, Sahin Aysegul, William Symmans, Lei Huo, Stacy Moulder. Serial TILs: Evaluating the role of mid-treatment tumor infiltrating lymphocytes (TIL) in predicting pathologic complete response (pCR) in early-stage triple negative breast cancer (TNBC) [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 P1-10-20.

BACKGROUND: Current treatment for early stage triple negative breast cancer (TNBC) includes neoadjuvant systemic chemotherapy (NAST), which is used to assess disease biology and the need for adjuvant treatment in case of residual disease at the time of surgery, also known as residual cancer burden (RCB). Patients with TNBC who experience RCB-0 (pathologic complete response [pCR]) or RCB-I after NAST have an excellent prognosis whereas patients with significant residual disease (RCB-II or RCB-III) are at a high risk of relapse. Standard NAST for TNBC achieves pCR in 30-50% of cases. NAST typically consists of anthracycline-based chemotherapy followed or preceded by a taxane +/- carboplatin. Disease progression (PD) is uncommon in TNBC patients receiving NAST and little is known regarding outcomes in patients who have PD during the initial phase of NAST. METHODS: Total 316 TNBC patients were evaluated from two prospectively accrued clinical trials of NAST (NCT02276443 and NCT01334021). The ARTEMIS trial (NCT02276443) aims to improve pCR rates by adding targeted therapy to chemotherapy as the second phase of NAST for those patients who do not experience at least a 70% volumetric reduction after 4 cycles of doxorubicin/cyclophosphamide (AC). Unique histopathologic features including % stromal tumor-infiltrating lymphocytes (sTIL), presence of mesenchymal histology (high vimentin expression by IHC), and androgen receptor expression are used to guide second phase therapy. RESULTS: 31 TNBC patients had PD while receiving AC as the first phase of NAST (10%; 95% CI= 6.69-13.31%). 9 of 31 patients proceeded to standard chemotherapy and all had RCB II/III disease. 22 of 31 patients were enrolled to targeted therapy trials. 6 were treated with the EGFR inhibitor panitumumab + carboplatin/paclitaxel, 9 with atezolizumab + nab-paclitaxel, and 7 with everolimus, bevacizumab, and liposomal doxorubicin (DAE). Of these 22 patients, 3 (13.6%) had pCR/RCB-0, 1 (4.5%) RCB-I and 18 (81.8%) had RCB II/III. All 4 patients who experienced RCB-0/I had T2N0 disease at diagnosis. 2 had sTIL < 5% and 2 patients had 70% sTIL. CONCLUSION: PD is uncommon while receiving NAST. Patients with TNBC and progression on initial NAST with AC are unlikely to achieve pCR or RCB-I status despite subsequent standard chemotherapy. Combination chemotherapy with targeted therapy on clinical trial resulted in a numerically higher rate of pCR+RCB-I (18%) as salvage therapy, but this was not statistically significant and requires confirmation in larger trials. Citation Format: Haven Garber, Gaiane Rauch, Beatriz Adrada, Rosalind Candelaria, Elizabeth Mittendorf, Alastair Thompson, Jennifer Litton, Senthil Damodaran, Bora Lim, Banu Arun, Naoto Ueno, Vicente Valero, Nuhad Ibrahim, Rashmi Murthy, Debu Tripathy, Helen Piwnica-Worms, Fraser Symmans, Lei Huo, Stacy Moulder. Residual cancer burden in patients with early stage triple negative breast cancer who progress on anthracycline-based neoadjuvant chemotherapy in an ongoing clinical trial (ARTEMIS) [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-16-09.

Background:While TNBC patients with pathologic complete response (pCR) or residual cancer burden (RCB-I) have good survival rates, those with extensive residual disease (RCB-II or RCB-III) after neoadjuvant chemotherapy (NACT) have poor prognosis. Patients without response to their first chemotherapeutic regimen have very low chance (5%) of achieving pCR. We have created a biomarker-driven drug development strategy, ARTEMIS (A Randomized, TNBC Enrolling trial to confirm Molecular profiling Improves Survival) to identify novel targeted therapies focusing on chemo-insensitive disease. The PI3K/Akt/mTOR pathway is a critical regulator of cell growth, apoptosis, metabolism in cancer cells and its activation is known to play an important role in resistance to chemotherapy. Clinical studies have shown that the combination of PI3K pathway inhibitors with taxanes are associated with improvement in response rates and survival. Alpelisib is approved for hormone receptor positive, HER2 negative, metastatic breast cancer patients with activating PIK3CA mutations. This study hypothesizes combination of alpelisib with nab-paclitaxel will improve PCR/RCB-1 in treatment-resistant early stage TNBC patients with activating PIK3CA or PTEN loss of function alterations. Trial Design: This will be a non-randomized, two- arm, open label, phase II study to evaluate the clinical activity of alpelisib and nab-paclitaxel in high-risk TNBC patients with PIK3CA or PTEN alterations with refractory or suboptimal response to anthracycline-based NACT. Eligibility criteria Stage 1-3 TNBC defined as ER Specific aims To determine if alpelisib in combination with nab-paclitaxel will improve rates of pathologic response (pCR/RCB-0 or RCB-I) from 5% to 20% in patients with chemotherapy insensitive TNBC with activating PIK3CA alterations (Arm-1) or PTEN loss of function alterations (Arm-2)To determine the radiographic response rate for alpelisib in combination with nab-paclitaxel in chemotherapy insensitive TNBC with PIK3CA (Arm-1) or PTEN (Arm-2) alterationsDetermine toxicity of alpelisib in combination with nab-paclitaxel given in the neoadjuvant settingDetermine progression free survival (PFS) at 3 years for patients treated with alpelisib in combination with nab-paclitaxel given in the neoadjuvant setting Statistical methods Primary objective is to determine if alpelisib in combination with nab-paclitaxel in the neoadjuvant setting will improve rates of pathologic response (counting pCR/RCB-0 or RCB-I as response) from 5% (control) to 20% (experimental arms). A Simon two-stage design will be employed with 12 patients in the first stage. If at least one patient has pCR/RCB-1, 25 more patients will be added for a total of 37 patients (alpha = beta = 10%). This design has a 54% probability of early termination after the first stage if the true pCR or RCB-I probability is 5%. Contact information for people with a specific interest in the trial sdamodaran@mdanderson.org Citation Format: Senthil Damodaran, Jennifer K Litton, Kenneth R. Hess, Colleen T. Eppig, Krzysztof J. Grzegorzewski, Funda Meric-Bernstam, Ignacio I. Wistuba, Jason B White, Gaiane M. Rauch, Rosalind P. Candelaria, Beatriz E. Adrada, Bora Lim, Stacy L. Moulder, Debu Tripathy. A phase-2 trial of neoadjuvant alpelisib and nab-paclitaxel in anthracycline refractory triple negative breast cancers with PIK3CA or PTEN alterations [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 OT2-06-01.

Background: FGFR1 gene amplifications occur in ~15% of invasive breast cancers (BCs) andhave been shown to be associated with endocrine therapy resistance, whereas FGFR2 amplifications occur in ~2% of invasive BCs (4% of triple-negative BCs [TNBCs]). Futibatinib is an oral, highly selective, irreversible FGFR1-4 inhibitor that has been shown to inhibit both mutant and wild-type FGFR isoforms. In a phase 1 study, futibatinib showed promising clinical activity and tolerability across tumor types, including BC. This phase 2 trial (FOENIX-MBC2) is designed to evaluate futibatinib alone or in combination with fulvestrant (a selective estrogen receptor down-regulator administered intramuscularly) in patients with metastatic BC. Trial design: FOENIX-MBC2 is a multicenter, phase 2, open-label, non-randomized study planned to be conducted in patients with locally advanced/metastatic BC harboring FGFR1/2 amplifications who have experienced disease progression after prior therapy for advanced/metastatic disease. Eligibility criteria include an Eastern Cooperative Oncology Group performance status of 0 or 1 and no prior FGFR inhibitor treatment. Approximately 168 patients are planned to be enrolled in one of four cohorts based on a recurrent BC diagnosis and FGFR amplification status (table) as determined by local testing. Patients will receive single-agent futibatinib (cohorts 1-3) or futibatinib plus fulvestrant (cohort 4) until disease progression, unacceptable toxicity, or other discontinuation criteria are met. Primary and secondary endpoints are detailed in the table. Sample sizes for cohorts 1, 2, and 3 are based on a Simon’s optimal 2-stage design; that for cohort 4 is based on a proof-of-concept phase 2 design. The anticipated start date is August 30, 2019. Patients, treatment, and endpoints in cohorts 1-4 of FOENIX-MBC2 CohortApprox. target enrollment (n)TreatmentKey patient inclusion criteriaEndpointsa1≤55FutibatinibHR+ HER2– BC, measurable disease per RECIST v1.1, FGFR2 amplification, and 1–3 prior endocrine therapies and ≤2 prior chemotherapy regimens for advanced/metastatic diseasePrimary: ORR Secondary: CBR, DOR, OS, PFS, 6-month PFS rate, safety2≤55FutibatinibTNBC, measurable disease per RECIST v1.1, FGFR2 amplification, and ≥1 prior chemotherapy or chemotherapy/immunotherapy regimen for advanced/metastatic diseasePrimary: ORR Secondary: CBR, DOR, OS, PFS, 6-month PFS rate, safety3≤24FutibatinibHR+ HER2– BC or TNBC; non-measurable, evaluable disease; FGFR2 amplification; and prior therapy as per cohort 1 (HR+ HER2– BC) or cohort 2 (TNBC)Primary: CBR Secondary: CR rate, DOR, OS, PFS, 6-month PFS rate, safety4≤34Futibatinib + fulvestrantHR+ HER2– BC, measurable disease per RECIST v1.1, high levels of FGFR1 amplification (FGFR1:CEN8 ratio ≥5.0 or FGFR1 copy number ≥10), and 1–2 prior endocrine-containing regimens and ≤1 prior chemotherapy regimen for advanced/metastatic disease, but no prior fulvestrantPrimary: 6-month PFS rate Secondary: ORR, CBR, DOR, OS, PFS, safetyCBR, clinical benefit rate; CR, complete response; DOR, duration of response; HER2-, human epidermal growth factor-negative; HR+, hormone-receptor-positive; ORR, objective response rate; OS, overall survival; PFS, progression-free survival; RECIST v1.1, Response Evaluation Criteria in Solid Tumors version 1.1aORR is defined as the proportion of all treated patients with a best overall response of CR or PR; CBR is defined as the proportion of all treated patients with a best overall response of CR, PR, or SD ≥24 weeks. ORR and CBR will be summarized descriptively. The 6-month PFS rate is the percentage of patients who remain alive and progression-free at 6 months estimated using the Kaplan-Meier method. This study is funded by Taiho Oncology, Inc. and Taiho Pharmaceutical Co., Ltd. Citation Format: Nick C. Turner, Ian E. Krop, Aditya Bardia, Senthil Damodaran, Miguel Martin, Karim A. Benhadji, Yaohua He, Mieke Ptaszynski, Carlos L. Arteaga. A phase 2 study of futibatinib (TAS-120) in metastatic breast cancers harboring fibroblast growth factor receptor (FGFR) amplifications (FOENIX-MBC2) [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 OT2-07-01.

PURPOSE Talazoparib has demonstrated efficacy in patients with BRCA-positive metastatic breast cancer. This study evaluated the pathologic response of talazoparib alone for 6 months in patients with a known germline BRCA pathogenic variant (g BRCA-positive) and operable breast cancer. METHODS Eligibility included 1 cm or larger invasive tumor and g BRCA-positive disease. Human epidermal growth factor receptor 2–positive tumors were excluded. Twenty patients underwent a pretreatment biopsy, 6 months of once per day oral talazoparib (1 mg), followed by definitive surgery. Patients received adjuvant therapy at physician’s discretion. The primary end point was residual cancer burden (RCB). With 20 patients, the RCB-0 plus RCB-I response rate can be estimated with a 95% CI with half width less than 20%. RESULTS Twenty patients were enrolled from August 2016 to September 2017. Median age was 38 years (range, 23 to 58 years); 16 patients were g BRCA1 positive and 4 patients were g BRCA2 positive. Fifteen patients had triple-negative breast cancer (estrogen receptor/progesterone receptor < 10%), and five had hormone receptor-positive disease. Five patients had clinical stage I disease, 12 had stage II, and three had stage III, including one patient with inflammatory breast carcinoma and one with metaplastic chondrosarcomatous carcinoma. One patient chose to receive chemotherapy before surgery and was not included in RCB analyses. RCB-0 (pathologic complete response) rate was 53% and RCB-0/I was 63%. Eight patients (40%) had grade 3 anemia and required a transfusion, three patients had grade 3 neutropenia, and 1 patient had grade 4 thrombocytopenia. Common grade 1 or 2 toxicities were nausea, fatigue, neutropenia, alopecia, dizziness, and dyspnea. Toxicities were managed by dose reduction and transfusions. Nine patients required dose reduction. CONCLUSION Neoadjuvant single-agent oral talazoparib once per day for 6 months without chemotherapy produced substantial RCB-0 rate with manageable toxicity. The substantive pathologic response to single-agent talazoparib supports the larger, ongoing neoadjuvant trial (ClinicalTrials.gov identifier: NCT03499353 ).

Background Radium‐223 dichloride (Ra‐223) is a targeted alpha therapy that induces localized cytotoxicity in bone metastases. We evaluated the efficacy and safety of Ra‐223 plus hormonal therapy in hormone receptor‐positive (HR+), bone‐dominant metastatic breast cancer. Methods In this single‐center phase II study, 36 patients received Ra‐223 (55 kBq/kg intravenously every 4 weeks) up to 6 cycles with endocrine therapy. The primary objective was to determine the clinical disease control rate at 9 months. Secondary objectives were to determine (a) tumor response rate at 6 months, (b) progression‐free survival (PFS) durations, and (c) safety. Results The median number of prior systemic treatments for metastatic disease was 1 (range, 0‐4). The disease control rate at 9 months was 49%. The tumor response rate at 6 months was 54% (complete response, 21%; partial, 32%). The median PFS was 7.4 months (95% CI, 4.8‐not reached [NR]). The median bone‐PFS was 16 months (95% CI, 7.3‐NR). There were no grade 3/4 adverse events. Conclusions Ra‐223 with hormonal therapy showed possible efficacy in HR+ bone‐dominant breast cancer metastasis, and adverse events were tolerable. We plan to further investigate the clinical application of Ra‐223 in these patients. (NCT02366130)., Radium‐223 dichloride is a targeted alpha therapy with localized cytotoxicity for bone metastasis.Our phase II trial which tested radium‐223 dichloride combined with hormonal therapy provided a high disease control with minimum toxicity in patients with hormone receptor‐positive, bone‐dominant metastatic breast cancer.

Summary HER2 mutations have been reported in approximately 2% of breast cancers. Regardless of HER2 overexpression or amplification status, breast cancer with HER2 mutations may respond to HER2-targeted therapy. As HER2 mutation is rare, the clinical and pathological features of HER2-mutated breast cancers, such as hormonal status, histological grade, and metastasis, remain poorly defined. Therefore, the identification of HER2-mutated breast cancer has clinical significance. We retrospectively screened patients with metastatic breast cancer in whom molecular profiling had been performed using next-generation sequencing from 2012 to 2015; we identified 18 patients with HER2 mutation. Mutations were found on next-generation sequencing-based panels, including Ion AmpliSeq Cancer Hotspot, Oncomine, FoundationOne, and Guardant360. HER2 mutations were identified in both the tyrosine kinase (n = 14) and extracellular (n = 4) domains. Of the 14 cases with tyrosine kinase domain mutations, 13 were estrogen receptor positive; the 4 cases with extracellular domain mutations were exclusively estrogen receptor negative. In addition, 11 of 14 patients with tyrosine kinase domain mutations had bone metastasis, whereas no patients with HER2 extracellular domain mutations had bone metastasis. Histologically, 13 patients had invasive ductal carcinoma, 1 had metaplastic carcinoma, and 4 had invasive lobular carcinoma (ILC). All 4 ILCs were high grade and pleomorphic, and not only had an HER2 mutation in the kinase domain but also had an HER2 mutation involving the L755 site. Specific mutation sites may be involved in the pathogenesis of nonclassic ILC.

Background: Folate receptor alpha (FRα) is a glycosyl phosphatidylinositol (GPI)-anchored cell surface protein that binds and internalizes folate, which is a cofactor required for DNA/RNA synthesis and cell growth and proliferation. There is a marked up-regulation of FRα in many solid tumors; in contrast, FRα has a minimal expression in adult normal tissue. Mirvetuximab soravtansine is an antibody drug conjugate (ADC) consisting of a maytansinoid, N2'-Deacetyl-N2'-(4-mercapto-4-methyl-1-oxopentyl)-maytansine (DM4), conjugated to an anti-FRα antibody, M9346A. Once bound to the FRα and internalized, the anti-mitotic agents are released and inhibit tubulin polymerization and microtubule assembly, leading to cell death. Here we report the expression of FRα+ on residual tumor samples in metastatic TNBC. Methods: 68 patients (Pts) with stage IV TNBC underwent prescreening to determine if residual tumor tissue expressed FRα. Formalin fixed paraffin embedded (FFPE) samples were sent to Ventana Translational Diagnostics CAP/CLIA Laboratory for analysis using an in-house developed assay, Ventana OptiView DAB Detection kit, and the Ventana BenchMark Ultra automated slide stainer. FRα expression was evaluated by board certified pathologists using a scoring scale 1+ (low), 2+ (medium), and 3+ (high). For the purposes of study entry, FRα expression on cell surface was required to be low, defined as >25% of cells having 1+ expression. Results: 12% (8/68) of evaluated TNBCs had moderate to high rates of FRα expression. The median age of pts screened for FRα was 53 years. Moderate to high FRα expression rates were more common in Black and Asian patients (Table 1). Conclusion: Our prospective study has demonstrated that moderate to high expression of FRα in metastatic TNBC is 12%, which is lower than previously reported. An ongoing phase II study will determine efficacy for mirvetuximab soravtansine in advanced TNBC. Acknowledgement: This study was approved and funded in part by the NCCN Oncology Research Program from general research support provided by ImmunoGen, Inc.

Background: Radium-223 dichloride (Ra-223) is a targeted alpha particle-based radiotherapeutic that has a localized cytotoxic effect on bone metastases. We sought to determine whether the circulating tumor cell (CTC) count and the presence of CTCs in epithelial-mesenchymal transition (EMT-CTCs) along with the standardized uptake value (SUV) on positron emission tomography-computed tomography (PET/CT) scans predict the efficacy of combined Ra-223 and hormonal therapy in patients with hormone receptor (HR)-positive bone-dominant metastatic breast cancer. Patients and Methods: In this single-center phase 2 study (NCT02366130), 36 patients received Ra-223 (55 kBq/kg intravenously) on day 1 and then every 4 weeks for six cycles. Patients also received a standard care endocrine monotherapy. One non-bone metastatic site was allowed. The number of prior endocrine therapies was not limited and one prior chemotherapy was allowed for metastasis. Response was evaluated using the PET Response Criteria in Solid Tumors (PERCIST) with PET/CT at baseline, 6 and 9 months (mo) later. The CTC count (CellSearch) and the presence of EMT-CTCs (AdnaTest) was determined at baseline, 6 and 9 mo later. Progression-free survival (PFS) time was calculated to evaluate efficacy. Results: Seven patients (20%) had a non-bone metastatic site. The median number of prior therapies for metastasis was 1 (range, 0-4). Six patients (17%) received chemotherapy. The median CTC count at baseline was 4 (range, 0-306). Only four patients (11%) were positive for EMT-CTCs at baseline. The median follow-up time was 14.7 mo (95% confidence interval [CI], 13.2 mo-not reached [NR]). The disease control rate at 9 mo was 46% in 33 patients who reached 9 mo or progressed up to 9 mo. The tumor response rate at 6 mo was 52% (complete/partialresponse rate; 22/30 %) in 27 patients whose disease was evaluable using PERCIST. The SUV on PET/CT decreased significantly at 6 and 9 mo after baseline (average decreases of 1.5 (p=0.0004) and 2.5 (p=0.0054), respectively). The median PFS duration was 7.4 mo (95% CI, 4.8 mo-NR). The median bone PFS was 16 mo (95% CI, 7.3 mo-NR). Patients with bone-only metastasis (N=28, 80%) had a significantly longer median PFS duration than did patients with non-bone metastases at baseline (N=7, 20%) (13.8 mo versus 4.5 mo; p=0.017). Patients without prior treatment (N=12, 34%) tended to have longer median PFS durations than did those who underwent prior treatment (N=23, 66%) (16.8 mo versus 4.8 mo; p=0.1865). Also, patients with Conclusions: Bone-only metastatic breast cancer and SUV suppression by Ra-223 are predictive of efficacy. Patients with baseline Citation Format: Ueno NT, Tahara RK, Reuben JM, Gao H, Saigal B, Fujii T, Lucci A, Ibrahim NK, Damodaran S, Shen Y, Liu DD, Hortobagyi GN, Tripathy D, Lim B, Chasen BA. CTCs and SUV to predict the efficacy of the bone-specific radiopharmaceutical agent radium-223 dichloride combined with hormonal therapy for hormone receptor-positive bone-dominant breast cancer metastasis [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-18-04.

Background: Serial biopsies (bx) of triple-negative breast cancer (TNBC) in the curative neoadjuvant setting provides critical information on dynamic changes in the tumor in response to neoadjuvant systemic therapy (NAST) and can help inform the development of novel therapeutic strategies. However, neoplastic seeding following image guided breast bx has previously been reported in TNBC, raising concerns that serial bx may worsen clinical outcomes. Thus, we sought to determine if serial bx were associated with poorer clinical outcomes (using rates of pathologic complete response [pCR]) in TNBC pts receiving NAST. Methods: We identified 370 TNBC pts who received NAST at MD Anderson Cancer Center from 2011-2017. 200 pts did not have any research bx done (controls) on the index breast carcinoma and 170 pts had at least one research bx done (cases) on the index breast carcinoma as part of the prospective molecular triaging ARTEMIS trial. Baseline characteristics were compared between cases and controls using the Student t-test, Wilcoxon Rank Sum test or Fisher's exact test as appropriate. Univariable and multivariable logistic regression was used to determine if rates of pCR following NAST were significantly different between cases and controls. Results: Demographic characteristics demonstrate no significant differences (Table). However, cases were more likely to have received an anthracycline (99% vs 96%, p=0.02) and a targeted agent (22% vs 0%, p Conclusion: This is the first study examining the impact of serial bx on clinical outcomes in TNBC pts in the curative neoadjuvant setting. Our data suggest that research bx in this setting do not compromise rates of pCR. Baseline and Treatment CharacteristicsCharacteristicControls (n=200)Cases (n=170)p valueMean age - years (standard deviation [SD])52 (12)53 (12)0.54Ethnicity White – n (%)113 (57)115 (68)0.09Black – n (%)48 (24)29 (17) Other – n (%)39 (20)26 (15) Mean tumor size – cm (SD)3.2 (1.4)3.3 (1.7)0.62T stage – n (%) T134 (17)35 (21)0.96T2145 (73)111 (65) T314 (7)17 (10) T47 (4)7 (4) N stage – n (%) N0101 (51)89 (52)0.83N170 (35)55 (32) N27 (4)6 (4) N322 (11)20 (12) Stage – n (%) I19 (10)21 (12)0.74II140 (70)113 (66) III41 (21)36 (21) Grade – n (%) 19 (5)00.14227 (14)22 (13) 3164 (82)148 (87) Neoadjuvant therapy – n (%) Anthracycline191 (96)169 (99)0.02Taxane199 (100)166 (98)0.18Platinum23 (12)23 (14)0.63Targeted agent037 (22) Citation Format: Yam C, Raghavendra A, Hess KR, Adrada BE, Candelaria RP, Damodaran S, Gilcrease MZ, Helgason T, Hortobagyi GN, Huo L, Layman RM, Lim B, Litton JK, Mittendorf EA, Murthy RK, Piwnica-Worms H, Rauch GM, Santiago L, Symmans F, Thompson AM, Tripathy D, Ueno NT, Valero V, Barcenas CH, Moulder SL, Yang W. Impact of serial biopsies in triple-negative breast cancer patients receiving neoadjuvant systemic therapy [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-15-06.

Advances in single cell copy number sequencing technologies have enabled the generation of data on hundreds to thousands of cells in parallel. Despite the rapid development in these technologies, there is a significant bottleneck for the analysis of the resulting large-scale datasets. Here we present CopyKit, a comprehensive and user-friendly toolkit for the analysis of single cell copy number data. CopyKit provides a suite of tools for pre-processing, QC, copy number inference, and subclone clustering to delineate the clonal diversity of tumors. We performed single cell copy number sequencing of 2977 cells from two breast tumor liver metastasis. CopyKit identified 4 and 12 subclonal populations, including amplification of PDGFRA, KRAS, and MYC as well as losses of PTEN, FOXO1, RB1, and BRCA1, many of which were spatially segregated in the tumor mass of the two tumors. Additionally, we applied CopyKit to study metastatic dissemination from a primary ER+ breast tumor with two matched metastatic sites and two colorectal carcinomas with matched liver metastatic tissues. This analysis demonstrated that the breast metastatic tumors selected for subclones that were lacking ERBB2 amplification in the primary site. Furthermore, the liver metastasis had deletions of chromosomes 18, 19, and 20p and a focal gain of FGFR1, while the pleural effusion acquired two additional focal gains on chromosome 8, including MYC. The colorectal metastatic tumors diverged from the primary tumor with copy number events affecting important cancer genes such as gain of SOX4, MYC, CDK8 and deletions of FHIT, CHEK1, and CHEK2. Collectively, this study shows that CopyKit provides a comprehensive set of tools for resolving clonal substructure from single cell copy number data for diverse applications in cancer biology. Citation Format: Darlan Conterno Minussi, Junke Wang, Aislyn Schalck, Yun Yan, Hua-Jun Wu, Cheng Peng, Min Hu, Emi Sei, Mary Edgerton, Hui Chen, Alejandro Contreras, David Hui, Senthil Damodaran, Scott Kopetz, Bora Lim, Nicholas Navin. Resolving clonal substructure from single cell genomic data in primary and metastatic tumors using CopyKit [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 1210.

Background: Trophoblast cell surface antigen (TROP2), is expressed on many tumors including breast cancer, thus TROP2 antibody drug conjugates are being pursued as a therapeutic strategy. Datopotamab deruxtecan (Dato-DXd) is composed of a humanized anti-TROP2 IgG1 monoclonal antibody attached to a highly potent topoisomerase I inhibitor payload (an exatecan derivative DXd) via a stable tetrapeptide-based cleavable linker. Dato-DXd has shown promise in the treatment of TROP2 expressing lung and breast cancers. However, the role of TROP2 as a predictor of therapeutic sensitivity is yet to be elucidated. We sought to determine efficacy of Dato-DXd in breast cancer patient-derived xenografts (PDXs) as well as explore biomarkers of response and combinations with PARP inhibitors. Methods: Membrane expression of TROP2 was assessed in 31 breast cancer PDXs and matching patient tumors by immunohistochemistry (IHC). Schlafen family member 11 (SLFN11) nuclear expression was also assessed by IHC. The antitumor efficacy of two doses (1 and 10 mg/kg, q3wk, IV) of Dato-DXd and the isotype control-DXd (IgG-DXd) were tested against 9 breast cancer PDXs derived from residual tumors after neoadjuvant chemotherapy. The PDXs represented a range of TROP2 expression levels, including 3 TROP2 negative/low PDXs. The antitumor activity of Dato-DXd in combination with PARP inhibition (olaparib) was assessed in 3 PDXs with intermediate Dato-DXd activity. Tumor volumes were measured twice weekly; antitumor activity was assessed by treatment-to-control ratio (T/C) and event-free survival (EFS-2). T/C ratio was calculated as (Vt,21/Vt,0)/(Vc,21/Vc,0), where t = treatment, c = control (no treatment or IgG-DXd), and V = tumor volume (mm3). Stable disease (SD) and response (R) were based on day 21 (-30- to 20% and Results: TROP2 H-score in PDXs correlated with TROP2 expression in matched patients (r= 0.7264, p50% SLFN11 positivity in the nucleus by IHC; 2 of 3 had doubling of EFS-2 both by Dato-DXd and IgG-DXd. The combination of Dato-DXd and olaparib had improved activity over single agents in 2 of 3 models. Additional comparative predictive and pharmacodynamic biomarker studies will be presented. Conclusion: Dato-DXd is a promising therapy for breast cancer patients including those resistant to standard chemotherapy. Additional biomarkers may better integrate DXd sensitivity into patient selection. Citation Format: Erkan Yuca, Kurt Evans, Argun Akcakanat, Gabriela Raso, Yasmeen Q. Rizvi, Fei Yang, Lauren Byers, Senthil Damodaran, Okajima Daisuke, Funda Meric-Bernstam. Anti-tumor activity and biomarker analysis for datopotamab deruxtecan in breast cancer PDX models [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 1768.