Tung, Nadine

501 Background: EA1181 (NCT04266249) is a single-arm trial of neoadjuvant THP for patients with clinical anatomic stage II/III HER2+ breast cancer; patients with cT4 or cN3 disease were excluded . Assessing the primary endpoint, 3-year recurrence-free survival in patients with a pCR (ypT0/Tis, ypN0), requires longer follow-up. Here, we present results for the secondary objective of pCR rate and its relation to clinicopathologic factors and the HER2DX pCR likelihood score (Reveal Genomics) derived from gene expression and clinical features. Methods: Patients received 4 cycles of trastuzumab and pertuzumab (HP) with weekly paclitaxel (12 weeks) or docetaxel (q3w x 4), followed by surgery. Clinicopathologic features were assessed for all patients and HER2DX pCR score (stratified by ER status) was determined using the diagnostic biopsy in a representative subset of study participants. Results: 2175 patients were enrolled. Median age was 55 years (range 22-88 years); 58% had clinical stage IIA, 33% stage IIB, and 9% stage III. 45% had nodal involvement (mostly cN1). 781 tumors were HER2+/ER- and 1394 HER2+/ER+ (locally tested ). 2141 patients started THP, for whom the pCR rate was 44% overall, 63.7% in HER2+/ER- and 32.4% in HER2+/ER+ tumors. Disease progressed during THP in 16 patients (0.7%). The pCR rate varied inversely to the proportion of cells staining for ER among patients with HER2+/ER+ breast cancer: 1-10%+, 62.5%; 11-69%, 51.6%; ≥70%, 22.5% (p <0.001). The pCR rate was significantly associated with higher grade, especially in HER2+/ER+ disease. T and N stage did not significantly affect pCR rate. Among 569 patients assessed for the HER2DX pCR score, the pCR rate was significantly greater for patients with a higher vs lower score, regardless of ER status (Table). Further correlations and interactions will be presented. Conclusions: Neoadjuvant THP resulted in pCR in nearly two-thirds of pts with clinical stage II/III HER2+/ER- and in one-third with HER2+/ER+ breast cancer. There was no association with clinical stage. Lower ER expression and higher grade were associated with higher pCR rates. The HER2DX pCR score was a significant predictor of pCR, regardless of ER status. Clinical trial information: NCT04266249 . All Participants HER2+/ER- HER2+/ER+ # patients enrolled pCR rate (95% CI) # patients enrolled pCR rate (95% CI) # patients enrolled pCR rate (95% CI) Evaluable Cohort 2141 44%(42-46%) 774 64%(60-67%) 1367 32%(30-35%) HER2DX Cohort 569 48%(44- 52%) 230 69% (63-75%) 339 34%(29-39%) HER2DX pCR-high score 182 (32%) 68%(60-74%) 147 (64%) 70% (62-77%) 36 (11%) 58%(41-74%) HER2DX pCR-medium score 161 (28%) 67% (59- 74%) 70 (30%) 74%(62- 84%) 89 (26%) 61%(50-71%) HER2DX pCR-low score 226 (40%) 19%(14- 25%) 13 (6%) 31%(9-61%) 214 (63%) 18%(13-24%) P-value HER2DX score <0.001 0.010 <0.001

PURPOSE Long-term outcomes of patients with stage I human epidermal growth factor receptor 2 (HER2)–positive breast cancer receiving adjuvant trastuzumab emtansine (T-DM1) remain undefined, and prognostic predictors represent an unmet need. METHODS In the ATEMPT phase II trial, patients with stage I centrally confirmed HER2-positive breast cancer were randomly assigned 3:1 to adjuvant T-DM1 for 1 year or paclitaxel plus trastuzumab (TH). Coprimary objectives were to compare the incidence of clinically relevant toxicities between arms and to evaluate invasive disease-free survival (iDFS) with T-DM1. Correlative analyses included the HER2DX genomic tool, multiomic evaluations of HER2 heterogeneity, and predictors of thrombocytopenia. RESULTS After a median follow-up of 5.8 years, 11 iDFS events were observed in the T-DM1 arm, consistent with a 5-year iDFS of 97.0% (95% CI, 95.2 to 98.7). At 5 years, the recurrence-free interval (RFI) was 98.3% (95% CI, 97.0 to 99.7), the overall survival was 97.8% (95% CI, 96.3 to 99.3), and the breast cancer-specific survival was 99.4% (95% CI, 98.6 to 100). Comparable iDFS was observed with T-DM1 irrespective of tumor size, hormone receptor status, centrally determined HER2 immunohistochemical score, and receipt of T-DM1 for more or less than 6 months. Although ATEMPT was not powered for this end point, the 5-year iDFS in the TH arm was 91.1%. Among patients with sufficient tissue for HER2DX testing (n = 187), 5-year outcomes significantly differed according to HER2DX risk score, with better RFI (98.1% v 81.8%, hazard ratio [HR], 0.10, P = .01) and iDFS (96.3% v 81.8%, HR, 0.20, P = .047) among patients with HER2DX low-risk versus high-risk tumors, respectively. CONCLUSION Adjuvant T-DM1 for 1 year leads to outstanding long-term outcomes for patients with stage I HER2-positive breast cancer. A high HER2DX risk score predicted a higher risk of recurrence in ATEMPT.

Abstract Background: Patients with HER2+ early breast cancer (EBC) and invasive residual disease (RD) after neoadjuvant therapy (NAT) have a higher risk of relapse than patients who have a pathologic complete response (pCR). Escalation of therapy in patients with RD using post-neoadjuvant T-DM1 has become the new standard of care, leading to improved invasive disease-free survival (iDFS), but patients with estrogen receptor (ER)-negative or nodal RD have suboptimal outcomes, and central nervous system recurrences are a challenge. More effective treatment strategies are urgently needed. Alliance A011801 (CompassHER2 RD) is an escalation trial for patients with high-risk HER2+ RD after neoadjuvant systemic therapy, evaluating the addition of the HER2 selective tyrosine kinase inhibitor (TKI) tucatinib to post-neoadjuvant T-DM1. Methods: Eligibility and Intervention: Patients with high-risk HER2+ RD (i.e., ER-, node-positive, or both) after a predefined course of neoadjuvant HER2-directed treatment are randomized 1:1 to adjuvant T-DM1 + placebo, vs. T-DM1 and tucatinib with adjuvant RT +/- ET. Eligibility criteria include completion of ≥ 6 cycles of NAT, including ≥ 9 weeks of paclitaxel and trastuzumab +/- pertuzumab. All chemotherapy (CT) must be completed preoperatively unless participating in EA1181 (~15-30% will be participants in the CompassHER2 pCR de-escalation companion trial [NCT04266249]; these patients must receive postoperative CT to complete ≥ 6 cycles prior to enrollment on A011801). Patients who received prior HER2-targeted TKIs or antibody-drug conjugates are ineligible. Objectives: The primary objective is to determine if iDFS is improved with addition of tucatinib to T-DM1 in patients with HER2+ EBC with RD after neoadjuvant systemic therapy; secondary endpoints include overall survival, breast cancer free survival, distant recurrence-free survival, brain metastases-free survival and disease-free survival. Correlative objectives include the association of i) tumor infiltrating lymphocyte (TILs) levels in the primary tumor and RD with iDFS, ii) TILs with tucatinib benefit, iii) iDFS and circulating tumor cells (CTC) at serial timepoints and iv) the magnitude of benefit of tucatinib (iDFS) in patients with/without detectable pretreatment CTCs. Quality of life and pharmacokinetic endpoints are also being evaluated. Statistics: A011801 is a prospective, double-blind, randomized, phase III superiority trial; stratified by i) receipt of postoperative CT (Y/N), ii) hormone receptor-status (+/-), and iii) pathologic lymph node status (+/-). The study targets an absolute difference of 5% in iDFS (control vs. experimental arm 82% & 87%, HR = 0.7), with a two-sided alpha of 0.05 and power of 80%. The sample size is 981; target accrual = 1031 patients; activation and estimated completion dates are 01/6/21 and ~ 01/2028. Accrual as of 7/10/2023: 438 patients. Support: U10CA180821, U10CA180882; Seagen Inc; https://acknowledgments.alliancefound.org. ClinicalTrials.gov Identifier: NCT04457596 Citation Format: Ciara O'Sullivan, Karla Ballman, Linda McCall, Tyler Zemla, Anna Weiss, Melissa Mitchell, Victoria Blinder, Nadine Tung, William Irvin, Myounghee Lee, Sailaja Kamaraju, Matthew Goetz, W. Fraser Symmans, Virginia Borges, Ian Krop, Ann Partridge, Lisa Carey. A011801 (CompassHER2 RD): Postneoadjuvant T-DM1 + tucatinib/placebo in patients with residual HER2-positive invasive breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-18-11.

ImportancePreventive bilateral salpingo-oophorectomy is offered to women at high risk of ovarian cancer who carry a pathogenic variant in BRCA1 or BRCA2; however, the association of oophorectomy with all-cause mortality has not been clearly defined.ObjectiveTo evaluate the association between bilateral oophorectomy and all-cause mortality among women with a BRCA1 or BRCA2 sequence variation.Design, Setting, and ParticipantsIn this international, longitudinal cohort study of women with BRCA sequence variations, information on bilateral oophorectomy was obtained via biennial questionnaire. Participants were women with a BRCA1 or BRCA2 sequence variation, no prior history of cancer, and at least 1 follow-up questionnaire completed. Women were followed up from age 35 to 75 years for incident cancers and deaths. Cox proportional hazards regression was used to estimate the hazard ratios (HRs) and 95% CIs for all-cause mortality associated with a bilateral oophorectomy (time dependent). Data analysis was performed from January 1 to June 1, 2023.ExposuresSelf-reported bilateral oophorectomy (with or without salpingectomy).Main Outcomes and MeasuresAll-cause mortality, breast cancer–specific mortality, and ovarian cancer–specific mortality.ResultsThere were 4332 women (mean age, 42.6 years) enrolled in the cohort, of whom 2932 (67.8%) chose to undergo a preventive oophorectomy at a mean (range) age of 45.4 (23.0-77.0) years. After a mean follow-up of 9.0 years, 851 women had developed cancer and 228 had died; 57 died of ovarian or fallopian tube cancer, 58 died of breast cancer, 16 died of peritoneal cancer, and 97 died of other causes. The age-adjusted HR for all-cause mortality associated with oophorectomy was 0.32 (95% CI, 0.24-0.42; P &amp;lt; .001). The age-adjusted HR was 0.28 (95% CI, 0.20-0.38; P &amp;lt; .001) and 0.43 (95% CI, 0.22-0.90; P = .03) for women with BRCA1 and BRCA2 sequence variations, respectively. For women with BRCA1 sequence variations, the estimated cumulative all-cause mortality to age 75 years for women who had an oophorectomy at age 35 years was 25%, compared to 62% for women who did not have an oophorectomy. For women with BRCA2 sequence variations, the estimated cumulative all-cause mortality to age 75 years was 14% for women who had an oophorectomy at age 35 years compared to 28% for women who did not have an oophorectomy.Conclusions and RelevanceIn this cohort study among women with a BRCA1 or BRCA2 sequence variation, oophorectomy was associated with a significant reduction in all-cause mortality.

Importance Magnetic resonance imaging (MRI) surveillance is offered to women with a pathogenic variant in the BRCA1 or BRCA2 gene who face a high lifetime risk of breast cancer. Surveillance with MRI is effective in downstaging breast cancers, but the association of MRI surveillance with mortality risk has not been well defined. Objective To compare breast cancer mortality rates in women with a BRCA1 or BRCA2 sequence variation who entered an MRI surveillance program with those who did not. Design, Setting, and Participants Women with a BRCA1 or BRCA2 sequence variation were identified from 59 participating centers in 11 countries. Participants completed a baseline questionnaire between 1995 and 2015 and a follow-up questionnaire every 2 years to document screening histories, incident cancers, and vital status. Women who had breast cancer, a screening MRI examination, or bilateral mastectomy prior to enrollment were excluded. Participants were followed up from age 30 years (or the date of the baseline questionnaire, whichever was later) until age 75 years, the last follow-up, or death from breast cancer. Data were analyzed from January 1 to July 31, 2023. Exposures Entrance into an MRI surveillance program. Main Outcomes and Measures Cox proportional hazards modeling was used to estimate the hazard ratios (HRs) and 95% CIs for breast cancer mortality associated with MRI surveillance compared with no MRI surveillance using a time-dependent analysis. Results A total of 2488 women (mean [range] age at study entry 41.2 [30-69] years), with a sequence variation in the BRCA1 (n = 2004) or BRCA2 (n = 484) genes were included in the analysis. Of these participants, 1756 (70.6%) had at least 1 screening MRI examination and 732 women (29.4%) did not. After a mean follow-up of 9.2 years, 344 women (13.8%) developed breast cancer and 35 women (1.4%) died of breast cancer. The age-adjusted HRs for breast cancer mortality associated with entering an MRI surveillance program were 0.20 (95% CI, 0.10-0.43; P &amp;lt; .001) for women with BRCA1 sequence variations and 0.87 (95% CI, 0.10-17.25; P = .93) for women with BRCA2 sequence variations. Conclusion and Relevance Results of this cohort study suggest that among women with a BRCA1 sequence variation, MRI surveillance was associated with a significant reduction in breast cancer mortality compared with no MRI surveillance. Further studies of women with BRCA2 sequence variations are needed to ascertain these women obtain the same benefits associated with MRI surveillance.

Abstract In the general population, physical activity has been associated with a lower risk of several cancers; however, the evidence for ovarian cancer is not clear. It is suggested that early-life physical activity may differentially impact risk. Whether this is true among women at high risk due to a pathogenic variant (mutation) in the BRCA1 or BRCA2 genes has not been evaluated. Thus, we performed a matched case–control study to evaluate the association between adolescent and early-adulthood physical activity and ovarian cancer. BRCA mutation carriers who completed a research questionnaire on various exposures and incident disease and with data available on physical activity were eligible for inclusion. Self-reported activity at ages 12–13, 14–17, 18–22, 23–29, and 30–34 was used to calculate the average metabolic equivalent of task (MET)-hours/week for moderate, vigorous, and total physical activity during adolescence (ages 12–17) and early-adulthood (ages 18–34). Conditional logistic regression was used to estimate the OR and 95% confidence intervals (CI) of invasive ovarian cancer associated with physical activity. This study included 215 matched pairs (mean age = 57.3). There was no association between total physical activity during adolescence (ORhigh vs. low = 0.91; 95% CI: 0.61–1.36; Ptrend = 0.85), early-adulthood (ORhigh vs. low = 0.78; 95% CI: 0.51–1.20; Ptrend = 0.38) and overall (ORhigh vs. low = 0.81; 95% CI: 0.54–1.23; Ptrend = 0.56) and ovarian cancer. Findings were similar for moderate (Ptrend ≥ 0.25) and vigorous (Ptrend ≥ 0.57) activity. These findings do not provide evidence for an association between early-life physical activity and BRCA-ovarian cancer; however, physical activity should continue to be encouraged to promote overall health. Significance: In this matched case–control study, we observed no association between physical activity during adolescence or early-adulthood and subsequent risk of ovarian cancer. These findings do not provide evidence for an association between early-life physical activity and BRCA-ovarian cancer; however, being active remains important to promote overall health and well-being.

PURPOSE Poly ADP-ribose polymerase inhibitors (PARPi) are approved for patients with human epidermal growth factor receptor 2–negative metastatic breast cancer (mBC) and germline pathogenic/likely pathogenic variant (hereafter mutation) in the BRCA1/ 2 genes (g BRCA); however, clinical benefit has also been demonstrated in mBC with somatic BRCA1/ 2 mutations (s BRCA) or germline PALB2 mutations (g PALB2). This study aims to describe the genomic landscape of homologous recombination repair (HRR) gene alterations in mBC and assess PARPi treatment outcomes for patients with g BRCA compared with other HRR genes and by status of a novel homologous recombination deficiency signature (HRDsig). METHODS A real-world (RW) clinico-genomic database (CGDB) of comprehensive genomic profiling (CGP) linked to deidentified, electronic health record–derived clinical data was used. CGP was analyzed for HRR genes and HRDsig. The CGDB enabled cohort characterization and outcomes analyses of 177 patients exposed to PARPi. RW progression-free survival (rwPFS) and RW overall survival (rwOS) were compared. RESULTS Of 28,920 patients with mBC, g BRCA was detected in 3.4%, whereas the population with any BRCA alteration or g PALB2 increased to 9.5%. HRDsig+ represented 21% of patients with mBC. BRCA and g PALB2 had higher levels of biallelic loss and HRDsig+ than other HRR alterations. Outcomes on PARPi were assessed for 177 patients, and g BRCA and s BRCA/ gPALB2 cohorts were similar: g BRCA versus s BRCA/g PALB2 rwPFS was 6.3 versus 5.4 months (hazard ratio [HR], 1.37 [0.77-2.43]); rwOS was 16.2 versus 21.2 months (HR, 1.45 [0.74-2.86]). Additionally, patients with HRDsig+ versus HRDsig– had longer rwPFS (6.3 v 2.8 months; HR, 0.62 [0.42-0.92]) and numerically longer rwOS (17.8 v 13.0 months; HR, 0.72 [0.46-1.14]). CONCLUSION Patients with s BRCA and g PALB2 derive similar benefit from PARPi as those with g BRCA alterations. In combination, HRDsig+, s BRCA, and g PALB2 represent an additional 19% of mBC that can potentially benefit from PARPi. Randomized trials exploring a more inclusive biomarker such as HRDsig are warranted.

Abstract Importance: The poly-adenosine diphosphate–ribose polymerase (PARP) enzymes are important for DNA single-strand break repair and PARP inhibitors (PARPi) cause an accumulation of unresolved DNA damage in tumors with BRCA1/2 mutations, resulting in cell death. However, because platinum salts also ultimately cause double-strand DNA breaks and may have overlapping mechanisms of resistance with PARPi, the efficacy of PARPi in patients with prior platinum therapy is unknown. Objective We sought to evaluate the efficacy of PARPi in patients with BRCA1/2-related breast cancer and previous platinum exposure. Data Sources: PubMed, Embase, and Cochrane Central Register of Controlled Trials databases were searched for papers up to June 26, 2022. Study Selection: We performed a systematic review and meta-analysis of studies that evaluated the efficacy of PARPi in patients with advanced or metastatic breast cancer and germline BRCA1/2 mutations. Two independent investigators identified double-blind, randomized controlled trials (RCTs) that included the subgroup of previous exposure to platinum. Data Extraction and Synthesis: Data extraction from published reports and quality assessment were performed under Cochrane recommendations. The software Review Manager 5.3 was selected for conducting the statistical analyses. Main Outcome(s) and Measure(s): The primary endpoint of interest was progression-free survival (PFS). Hazard ratios (HRs) with a 95% confidence interval (CI) were pooled, and a p-value of < 0.05 was considered statistically significant. Results From 2,069 database results (487 on PubMed; 1,376 on Embase; and 206 on Cochrane), 42 studies were fully reviewed, and 4 RCTs (total of 249 patients) were included in the final investigation. The PARPi included were Olaparib, Talazoparib, Niraparib, and Veliparib. Pooled analysis showed that PARPi improved PFS in breast cancer patients with prior treatment with platinum-based therapy compared to the control group [HR = 0.72; 95% CI, 0.53–0.97; p = 0.03]. For comparison, the population without previous platinum exposure had a similar magnitude of benefit from PARPi [HR = 0.68; 95% CI, 0.52–0.89; p = 0.005]. Conclusions and Relevance: Despite the concerns about cross-resistance between PARPi and platinum agents, patients with advanced breast cancer and previous exposure to platinum therapy have a longer PFS with PARPi when compared to standard chemotherapy.

Abstract Background: The ATEMPT trial primary analysis found that one year of adjuvant trastuzumab emtansine (T-DM1) achieved a 3-year iDFS of 97.8% for patients with stage I HER2+ breast cancer, but was not associated with fewer clinically relevant toxicities (CRTs) compared with paclitaxel and trastuzumab (TH). In this end-of-study analysis, we report 5-year survival outcomes and correlative analyses from the trial. Methods: Patients with stage I centrally confirmed HER2+ breast cancer were randomly assigned 3:1 to adjuvant T-DM1 for one year or TH and received T-DM1 3.6 mg/kg IV every 3 weeks for 17 cycles or paclitaxel 80 mg/m2 IV with weekly trastuzumab IV followed by trastuzumab for 9 months. The co-primary objectives were to compare the incidence of CRTs between the 2 arms and to evaluate iDFS in patients receiving T-DM1. To investigate proteomic correlates of recurrence, spatial proteomic analyses were performed on samples from 13 patients experiencing iDFS events (cases) and 24 matched controls using the NanoString GeoMx Digital Spatial Profiler. The impact of HER2 heterogeneity on outcomes was investigated among 17 cases and 51 matched controls by fluorescence in-situ hybridization (FISH). HER2 genetic heterogeneity was assessed by scrutinizing the whole tumor area and defined as the occurrence of HER2 gene amplification in &gt;5% but &lt; 50% invasive tumor cells. The risk of recurrence was evaluated centrally with the HER2DX genomic assay from 225 primary tumor samples. Germline whole genome sequencing (WGS) was conducted among 55 patients experiencing T-DM1-induced thrombocytopenia and/or bleeding and 55 matched controls to identify genomic correlates for this side effect. Results: A total of 497 patients who initiated protocol therapy were included in this analysis (383 T-DM1 and 114 TH). After a median follow up 5.8 years, among patients receiving T-DM1 there were a total of 11 iDFS events, with 3 distant recurrences. The 5-year iDFS for T-DM1 was 97.0% (95% CI, 95.3-98.8%), the 5-year recurrence-free interval (RFI) was 98.6% (95% CI: 97.4-99.8%) and the 5-year overall survival (OS) for T-DM1 was 97.8 % (95% CI, 96.3-99.3%). Although the study was not powered to evaluate the efficacy of TH, among the 114 patients receiving TH, a total of 9 iDFS events were observed, including 2 distant events; the 5-year iDFS with TH was 91.3% (95% CI: 86.0-96.9%), 5-year RFI was 93.3% (95% CI: 88.6-98.2%) and 5-year OS was 97.9% (95% CI: 95.2-100%). A total of 56 samples were evaluable for heterogeneity analyses, among which 14% (n=8) harbored HER2 genetic heterogeneity. Spatial proteomic analyses found that NF1 (adjusted p=0.72 × 10-6) and CTLA-4 (adjusted p=0.15 × 10-3) were significantly upregulated in primary samples from cases, while cleaved caspase 9, CD25, GITR, ICOS, p53 and PD-L2 were significantly upregulated in controls (all with adjusted p&lt; 0.05). Germline WGS found that the top gene associations with thrombocytopenia and thrombocytopenia or bleeding were ALMS1 (p=0,19 × 10-3) and APBA3 (p=0,23 × 10-3), respectively, although none reaching the threshold for genome wide significance. rs62143195 and rs114169776 were the top single nucleotide polymorphisms associated with thrombocytopenia and thrombocytopenia or bleeding, respectively. Data on the impact of HER2 heterogeneity and of HER2DX score on survival outcomes will be presented. Conclusion: With longer follow-up, adjuvant T-DM1 confirmed outstanding long-term outcomes among patients with stage I HER2+ breast cancer, demonstrating a 5-year RFI of 98.6%. Spatial proteomic analyses identified a potential association between NF1 and CTLA-4 expression with recurrence. Details on the impact of HER2 heterogeneity and HER2DX assay on prognosis will be presented. Citation Format: Paolo Tarantino, Nabihah Tayob, Chau T Dang, Denise Yardley, Steven J. Isakoff, Vicente Valero, Meredith Faggen, Therese Mulvey, Ron Bose, Douglas Weckstein, Antonio C. Wolff, Katherine Reeder-Hayes, Hope Rugo, Bhuvaneswari Ramaswamy, Dan Zuckerman, Lowell Hart, Vijayakrishna K. Gadi, Michael Constantine, Kit Cheng, Audrey Merrill Garrett, Paul K. Marcom, Kathy S. Albain, Patricia DeFusco, Nadine Tung, Blair Ardman, Rita Nanda, Rachel C. Jankowitz, Mothaffar Rimawi, Vandana Abramson, Paula R. Pohlmann, Catherine Van Poznak, Andres Forero-Torres, Minetta C. Liu, Kathryn Ruddy, Yue Zheng, Romualdo Barroso-Sousa, Adrienne Waks, Michelle K. DeMeo, Molly K. DiLullo, Giuseppe Curigliano, Harold Burstein, Ann Partridge, Eric Winer, Giuseppe Viale, Winnie Hui, Elizabeth A. Mittendorf, Bryan P. Schneider, Aleix Prat, Ian Krop, Sara Tolaney. Adjuvant Trastuzumab Emtansine Versus Paclitaxel plus Trastuzumab for Stage I HER2+ Breast Cancer: 5-year results and correlative analyses from ATEMPT (TBCRC033) [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 PD18-01.

Abstract Background Breast cancers in women with a germline BRCA1/2 mutation (gBRCAm) have homologous recombination deficiency (HRD) and are sensitive to therapies causing double-strand DNA breaks. In TBCRC 031 (INFORM), both neoadjuvant cisplatin and doxorubicin/cyclophosphamide (“AC”) in gBRCAm carriers resulted in a complete pathologic response in 18% and 26% respectively in patients with newly diagnosed HER2–negative breast cancer. Herein, we describe molecular features from tumor whole exome (WES) and transcriptome sequencing (RNAseq) associated with response. Methods TBCRC 031 (the INFORM Trial - NCT01670500) was a randomized phase II neoadjuvant trial comparing the efficacy of cisplatin versus AC in gBRCAm carriers with stage I-III HER2–negative breast cancer. Of 118 patients enrolled, 92 patients provided fresh frozen research biopsies, collected prior to chemotherapy initiation, which were subjected to WES and RNAseq. Variants were called using GATK best practices and intratumoral heterogeneity was inferred from mutations and variant allele frequencies using Mutant Allele Tumor Heterogeneity (MATH) scores. Mutational Signature 3 (Sig3) and Genomic Instability Score (GIS) were calculated with SigMA and scarHRD, respectively. RNAseq data were utilized to perform differential gene expression and functional analyses, while cellular deconvolution was performed with CIBERSORTx trained against breast cancer single cell data. Patients were grouped according to their residual cancer burden (RCB) as responders (RCB-0 or 1), or non-responders (RCB-2 or 3). P-values ≤ 0.05 were considered statistically significant and when appropriate, adjustment for multiple testing was performed using a false discovery rate ≤ 5%. Results Of the 92 patients with gBRCAm, 59 (64%) had triple-negative and 33 (36%) were hormone-receptor positive HER2-negative breast cancer, 40 (43%) were classified as responders and 52 (57%) as non-responders. WES analysis revealed that indices of HRD were high (Sig3 exposure predominant and GIS ≥ 42) across most samples irrespective of receptor status and not significantly different among responders and non-responders. In contrast, responders exhibited lower levels of intratumor heterogeneity than non-responders (median MATH 42.9 vs. 33.5, p = 0.01). 223 genes were differentially expressed between responders and non-responders following control for tumor hormone receptor status, BRCA1/2 mutation, and menopausal status. Pathways identified as significantly enriched in upregulated genes were indicative of intrinsic immune activation in responders (e.g., T-cell activation, immune response-signaling, and regulation of leukocyte activation). Cellular deconvolution of the tumor microenvironment confirmed that responders presented a higher proportion of T-cells (p = 0.025) and myeloid cells (p = 0.003) in the tumor samples, while perivascular-like cells were enriched in non-responders (p = 0.034). Conclusion In this analysis of the largest cohort of treatment-naïve gBRCAm breast cancer to date, we found that response to cytotoxic chemotherapy is associated with a transcriptional program of intrinsic immune activation and an increased population of intratumoral T-cells and myeloid cells. Lower levels of intratumor heterogeneity and higher immune activation were associated with response to chemotherapy gBRCAm carriers while HRD scores were not. Citation Format: Felipe Batalini, Doga C. Gulhan, Xanthi Lida Katopodi, Nikolas Kalavros, Antuan Tran, Dimitra Karagkouni, Emily Stern-Gatof, Stuart Schnitt, Judy E. Garber, Gerburg M. Wulf, Peter J. Park, Ioannis Vlachos, Nadine Tung. Intratumor heterogeneity and intrinsic immune activation are associated with response to chemotherapy in BRCA-related breast cancers [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 P5-12-03.