BRCA1 Tumor Research Articles

Prevalence and clinical impact of tumor BRCA1 and BRCA2 mutations in patients presenting with localized or metastatic hormone-sensitive prostate cancer.

The appropriate management of localized or metastatic hormone-sensitive prostate cancer (HSPC) patients harboring tumor BRCA mutations (tBRCAm) is not well-characterized. We sought to evaluate the prevalence and clinical outcomes of patients with tBRCAm and localized or de novo metastatic HSPC. We performed a multicenter, international, retrospective cohort study of localized (cohort 1) and de novo metastatic (cohort 2) HSPC patients who underwent tumor BRCA1 and BRCA2 sequencing from 2013 to 2019. Primary endpoints included event-free survival (EFS) and metastases-free survival (MFS) for cohort 1, and time to castration-resistant prostate cancer (TTCRPC) and overall survival (OS) for cohort 2. Kaplan-Meier method and Cox regression models estimated the association of endpoints with tBRCA status. Of 399 identified patients with localized and de novo metastatic HSPC who underwent tumor BRCA1 and BRCA2 sequencing, 3.1% (8/258) patients of cohort 1 and 10.6% (15/141) patients of cohort 2 harbored tBRCAm. The median follow-up was 33 and 36 months, respectively. In cohort 1, median EFS was 18.1 vs. 57 months (p = 0.28) and MFS was 37 vs. 153.4 months (p = 0.08) for patients with tBRCAm compared to patients with no tBRCAm. In cohort 2, the TTCRPC was 24 vs. 19 months (p = 0.65) and OS was 64 vs. 60 months (p = 0.95) in patients with and without tBRCAm, respectively. While tBRCAm seems to be associated with greater relapse risk in localized disease, tBRCAm did not influence the clinical outcomes of patients presenting with de novo metastatic HSPC treated with conventional therapies. tBRCAm may exert different prognostic effects across the clinical spectrum of prostate cancer.

BRCA Genetic Test and Risk-Reducing Salpingo-Oophorectomy for Hereditary Breast and Ovarian Cancer: State-of-the-Art.

Simple SummaryThe BRCA genetic test and HRD (homologous recombination deficiency) test are used as a companion diagnosis before starting PARP (poly ADP-ribose polymerase) inhibitor treatment. In clinical practice, gynecologists treating ovarian cancer are faced with decisions such as whether to recommend germline BRCA (gBRCA) test to all ovarian cancer patients and whether to do the gBRCA test first or HRD test first. Regarding the judgment result of the HRD test, the cutoff value differs depending on the clinical trial, and the prevalence of gBRCA pathogenic variant rate is different in each histological type and country. RRSO (risk reducing salpingo-oophorectomy) may have possibly reduced the risk of breast cancer for BRCA2 pathogenic variant carriers but not for BRCA1 carriers.In the field of gynecology, the approval of the PARP inhibitors (PARPi) has been changing the treatment of ovarian cancer patients. The BRCA genetic test and the HRD test are being used as a companion diagnosis before starting PARPi treatment. BRACAnalysis CDx® and Myriad myChoice® HRD test are widely used as a BRCA genetic test and HRD test, respectively. In addition, FoundationOne®CDx is sometimes used as a tumor BRCA test and HRD test. In clinical practice, gynecologists treating ovarian cancer are faced with making decisions such as whether to recommend the gBRCA test to all ovarian cancer patients, whether to perform the gBRCA test first or HRD test first, and so on. Regarding the judgment result of the HRD test, the cutoff value differs depending on the clinical trial, and the prevalence of gBRCA pathogenic variant rate is different in each histological type and country. A prospective cohort study showed that RRSO reduced all-cause mortality in both pre- and postmenopausal women; however, RRSO significantly reduced the risk of breast cancer for BRCA2 pathogenic variant carriers, but not for BRCA1 pathogenic variant carriers. Moreover, salpingectomy alone is said to not decrease the risk of developing ovarian or breast cancer, so further discussion is evidently required. We discuss the current situation and problems in doing BRCA genetic test and RRSO in this review article.

BRCA reversion mutations in a pan-cancer cohort to reveal BRCA-dependence in select noncanonical BRCA-mutant histologies.

3012 Background: Loss of BRCA1/2 function leads to homologous recombination deficiency (HRD) and can enhance platinum and PARP inhibitor sensitivity in breast, pancreas, prostate, and ovarian cancers. In BRCA-associated cancers, resistance can result from the development of BRCA1/2 reversion mutations, which restore BRCA1/2 function. By contrast, a BRCA mutation may be an incidental finding in other tumor histologies. Methods: To determine the distribution of reversion mutations in a pan-cancer cohort, the MSK-IMPACT clinical sequencing cohort was mined to identify patients who had both a germline BRCA1/2 mutation and a frameshift somatic reversion mutation that restored BRCA1/2 function. Whole exome resequencing was used to detect HRD signatures. Chart review enabled collection of data on treatment history in patients consented to germline testing. Results: Of the 33,277 patients with matched tumor and normal sequencing profiled in this study, 861 patients were found to have germline pathogenic BRCA1/2 alterations, including 347 (40%) in BRCA1 and 514 (60%) in BRCA2. Somatic BRCA1/2 driver alterations were also found in tumor tissue from an additional 447 patients, with 156 (35%) having BRCA1 mutations, and the remainder having alterations in BRCA2 (65%) . Among the 1,308 germline or somatic BRCA1/2 mutant tumors, we identified reversion mutations in 12 patients, all of whom were germline carriers of BRCA1/2, comprising 3 BRCA1 and 9 BRCA2 tumors. 7 patients consented to germline testing enabling review of clinical characteristics and treatment history, 5 of whom received PARP inhibitor or platinum-therapy prior to reversion detection. Ten of 12 tumors with reversion mutations were in canonical BRCA-associated cancers. Interestingly, reversion mutations were also found in patients with lung adenocarcinoma (n=1) and gastroesophageal junction adenocarcinoma (n=1). In both these non-canonical histologies, the reversion was detected following progression on platinum-based therapy. Whole exome resequencing of the lung tumor revealed the classic somatic molecular phenotypes of HRD that are characteristic of BRCA-dependent tumors, including in terms of large-scale transitions, HRD-loss of heterozygosity, signature 3, and the number of telomeric allelic imbalance score. Conclusions: Matched tumor and normal sequencing from a large cohort of patients with diverse cancer histologies reveals that reversion mutations are found across BRCA-associated cancer types. In rare cases, reversion mutations in BRCA1/2 following platinum-based therapy may be indicative of prior BRCA-dependence in select non-canonical tumor histologies.

Progression-free survival (PFS) and second PFS (PFS2) by disease stage in patients (pts) with homologous recombination deficiency (HRD)-positive newly diagnosed advanced ovarian cancer receiving bevacizumab (bev) with olaparib/placebo maintenance in the phase III PAOLA-1/ENGOT-ov25 trial.

5514 Background: In the Phase III PAOLA-1/ENGOT-ov25 trial (NCT02477644), the addition of maintenance olaparib to bev in pts with newly diagnosed advanced high-grade ovarian cancer (HGOC) resulted in a significant PFS benefit, particularly in HRD-positive (HRD+) pts (hazard ratio [HR] 0.33; 95% CI 0.25–0.45) (Ray-Coquard et al. NEJM 2019). We explored efficacy in HRD+ pts by disease stage. Methods: Pts with newly diagnosed, FIGO stage III–IV HGOC in response after platinum-based chemotherapy + bev received bev (15 mg/kg q3w for 15 months [mo]) + either olaparib (300 mg bid for 24 mo) or placebo (pbo). This exploratory analysis evaluated PFS (data cut-off [DCO]: Mar 22 2019) and PFS2 (DCO: Mar 22 2020) in HRD+ pts (tumor BRCA1/ BRCA2 mutation [tBRCAm] or genomic instability score [Myriad myChoice HRD Plus] ≥42) by FIGO stage. Results: 387/806 randomized pts (48%) were HRD+; 272/387 (70%) had stage III disease and 115/387 (30%) had stage IV disease. 153 (56%) HRD+ stage III pts and 61 (53%) HRD+ stage IV pts had a tBRCAm. Among HRD+ stage III pts, 172 (63%) had upfront surgery (51/172 [30%] had residual disease) and 90 (33%) had interval surgery (19/90 [21%] had residual disease); 52 (45%) HRD+ stage IV pts had upfront surgery (34/52 [65%] had residual disease) and 55 (48%) had interval surgery (18/55 [33%] had residual disease). Median follow-up for PFS and PFS2 was respectively 24.8 and 37.2 mo in HRD+ stage III pts and 24.0 and 37.0 mo in HRD+ stage IV pts. Median PFS, PFS2 and HRs are in the Table. Among HRD+ stage III pts, 36-mo PFS2 (olaparib + bev vs pbo + bev) was 74% vs 60%; among HRD+ stage IV pts, 53% vs 30%. Among HRD+ stage III pts with no residual disease after upfront surgery, HR (95% CI) for PFS was 0.15 (0.07–0.30) and for PFS2 was 0.22 (0.06–0.67). Among HRD+ stage III pts with residual disease after upfront surgery or who received neoadjuvant chemotherapy, or HRD+ stage IV pts, HR (95% CI) for PFS was 0.38 (0.27–0.53) and PFS2 was 0.68 (0.46–1.03). Conclusions: In the PAOLA-1 study, maintenance olaparib + bev provided a PFS and PFS2 benefit over pbo + bev in HRD+ pts, irrespective of FIGO stage and residual disease after upfront surgery. Clinical trial information: NCT02477644. [Table: see text]

Association of ATM mutations in metastatic prostate cancer with differential genomic alteration profiles from homologous recombination deficient and proficient tumors.

5063 Background: ATM mutations, one of a family of DNA repair defects prevalent in prostate cancer, have been included in a list of actionable mutations for PARP inhibitor (PARPi) therapeutic trials. Despite preclinical evidence, PARPi have shown minimal clinical activity in ATM mutant prostate cancer (ATMmPCa). The present analysis explores co-occurring genomic alterations that may drive outcomes of metastatic PCa (mPCa) patients with tumors harboring ATM mutations and provide clues for understanding therapy resistance and potential targets. Methods: This study included molecular profiling analysis of 1375 cases of mPCa. Tumors were analyzed using next-generation sequencing (NGS), whole transcriptome sequencing (WTS), and immunohistochemistry (IHC) (Caris Life Sciences, Phoenix, AZ). dMMR/MSI-H status was determined by IHC, NGS, and fragment analysis and tumor mutational burden (TMB) was calculated based on somatic nonsynonymous missense mutations. We performed differential gene expression analysis of HR-associated transcripts such as ATR, PARP1-3, RAD50, RAD51A/B/C/D and RAD54. Significance was determined using the ꭓ2 test and Benjamini-Hochberg method. Results: Fifty-nine (4.2%) cases harbored pathogenic ATM mutations, 84 (6.2%) harbored BRCA2 mutations. 1018 tumors (74%) were deemed homologous recombination proficient (HRP) and 155 tumors (11.3%) were HR Deficient (HRD); harboring one or more mutation in HR-related genes excluding ATM and BRCA2. The mutation rate of TP53 was significantly lower in ATMmPCa (12.0%) compared to BRCA2mPCa (35%), HRD (35%) and HRP (46.6%) tumors. ATMmPCa showed higher rates of SMAD2 (3.7%/1%) and FLCN (5.2%/0.3%) alterations compared to HRP cases. PARP1 and RAD51D gene expression was reduced in ATMmPCa compared to HRP (p < 0.05) and BRCA2mPCa ( p < 0.05) tumors, respectively. No differences in gene expression levels were detected for ATR, PARP2, PARP3, RAD50, and RAD54. Chromosomal segments demonstrating differential CNA in ATMmPCa vs HRP, HRD, or BRCA2mPCa included FGF19, FGF4, PTPN11, ALDH2, DAXX, BCL7A, CCND1, BMPR1A and MEF2B (Q-value < 0.05 determined by ꭓ2). The most common CNA in ATMmPCa was CCND1, present in approximately 13% (7/55) of cases. Compared to BRCA2mPCa and HRD cases, ATMmPCa cases are less likely to display markers of immunotherapy response such as dMMR/MSI-H or TMB ≥10 mutations/MB. Conclusions: ATMmPCa demonstrated several differences in co-occurring alterations compared to BRCA2mPCa, HRD and HRP mPCa. ATMmPCa tumors were less likely to harbor alterations in TP53 compared to BRCA2, HRD or HRP tumors. CNA in ATMmPCa occurred in 9 genes across distinct mPCa molecular subtypes and were enriched for those associated with the 11q13 amplicon harboring Cyclin D1. The FGF and PTPN11 related pathways are potentially targetable pathways in ATMmPC and may merit further study.

Integration of molecular cancer classification and next-generation sequencing to identify metastatic patients eligible for PARP inhibitors.

e15080 Background: Olaparib, rucaparib, and niraparib are 3 poly-ADP-ribose polymerase inhibitors (PARPi) approved by the FDA for ovarian, breast, pancreatic, prostate, fallopian tube and peritoneal cancers with BRCA mutations. Several ongoing clinical trials aim to determine the efficacy of PARPi in various other cancer types, including specific cancer subtypes, such as clear cell renal cell carcinoma and cholangiocarcinoma either as monotherapy or combination therapy; however, eligibility for PARPi therapy requires the identification of the primary tumor type and confirmation of BRCA mutation. The 92-gene assay (CancerTYPE ID) is a validated gene expression classifier of 50 tumor types and subtypes for metastatic patients with unknown or uncertain diagnoses. Multimodal biomarker testing, including next-generation sequencing (NGS), enables identification of actionable biomarkers to guide targeted therapy selection. In the current study, a database of metastatic cases that integrates tumor type with biomarker analysis was characterized to identify those eligible for PARPi treatment. Methods: MOSAIC (Molecular Synergy to Advance Individualized Cancer Care) is an IRB-approved, de-identified database of cases submitted for CancerTYPE ID testing with tissue-guided multimodal biomarker testing by NGS, including tumor mutational burden (TMB) fluorescent in situ hybridization (FISH), and microsatellite instability (MSI), and immunohistochemistry (IHC) (NeoTYPE profiles, Neogenomics). For the current study, metastatic cancers classified as ovarian, breast, pancreatic, or prostate were identified in the database, followed by NGS analysis to detect mutations in BRCA1 or BRCA2. Results: The current analysis included 2151 CancerTYPE ID cases, from which 71 ovarian, 47 breast, 12 pancreatic and 15 prostate cancer cases were identified. Out of 46 cases of ovarian cancer with molecular biomarker results, NGS identified 7 (15.3%) cases with BRCA1 mutation and 4 (8.7%) cases with BRCA2 mutation. Additionally, 4 (10.5%) cases with BRCA1 mutation and 1 (2.6%) case with BRCA2 mutation out of 38 cases of breast cancer with BRCA results were detected. No cases of prostate cancer or pancreatic cancer with mutations in BRCA1 or BRCA2 were detected. Conclusions: These findings in metastatic patients demonstrate the clinical utility of tumor type identification combined with molecular biomarker profiling, leading to additional options for patients with advanced disease. Specifically, analysis of the MOSAIC database identified a subset of patients with metastatic cancers eligible for PARPi therapy based on tumor type and BRCA mutation status. As new and approved PARPi are evaluated for efficacy in additional tumor types, patients can be identified that may be eligible for these targeted cancer drugs.

Pathological complete response rate and survival in patients with BRCA-associated triple-negative breast cancer after 12 weeks of de-escalated neoadjuvant chemotherapy: Translational results of the WSG-ADAPT TN randomized phase II trial (NCT01815242).

579 Background: The phase II trial WSG-ADAPT TN randomized triple-negative breast cancer (TNBC) patients to receive 12 weeks of neoadjuvant nab-paclitaxel (nab-pac) combined with carboplatin (carbo) vs gemcitabine (gem) and showed a substantial improvement of pathological complete response (pCR: ypT0/is, ypN0) with carbo (45.9% vs 28.7%). pCR had a strong favorable impact on iDFS after 3-year follow-up. Distribution of tumor mutations in BC-associated genes and impact of BRCA mutation status on pCR and outcome are analyzed here. Methods: NGS-based mutational analysis of BRCA1/2 and 18 further (potentially) BC-associated genes was performed on DNA derived from pretreatment FFPE samples (gem: n = 158, carbo: n = 108) using a customized gene panel. Variants with a variant fraction of ≥5% were included and classified according to IARC and ENIGMA guidelines. Results: In 42 of the 266 analyzed samples, at least one deleterious BRCA1/2-variant was found (15.8%; BRCA1 n = 37, BRCA2 n = 3, BRCA1+ BRCA2 n = 2) one of which displayed an additional STK11-mutation. In the BRCA1/2-negative cohort, a mutation in one of 14 further analyzed (potential) BC-risk genes was found in 19 samples (7.1%; BARD1 n = 3, CHEK2 n = 2, CDH1 n = 2, FANCM n = 3, PALB2 n = 5, RAD50 n = 1, RAD51C n = 1, RAD51D n = 1, XRCC2 n = 1; no deleterious mutations were found in ATM, BRIP1, MRE11A, NBN). At least one deleterious variant in TP53, PIK3CA, PTEN or MAP3K1 was seen in 89.1% (n = 237; TP53 n = 233, PIK3CA n = 22 PTEN n = 15, MAP3K1 n = 1). In 22 samples (8.3%) no deleterious mutation was identified in the analyzed genes. Overall, patients with tumor BRCA mutation (carbo n = 14, gem n = 28) had 45.2% vs 34.4% pCR (OR = 1.58, 95%-CI: 0.81-3.07, p =.18) without a mutation. pCR in the small group with mutation receiving carbo (n = 14) was 64.3% vs. 34.5% in all others (OR = 3.41, 95%-CI: 1.11-10.50; p =.03); direct comparison to BRCA-positive patients receiving gem (n = 28, 35.7%, OR = 3.2, 95%-CI: 0.85-12.36, p = 0.079) did not reach statistical significance. The results suggest that the strong favorable impact of pCR on iDFS is preserved even among BRCA-positive patients (n = 42, p =.07), as well as in the BRCA-negative subgroup (p <.001). No evidence for a predictive impact of BRCA mutation on efficacy of 4xEC additional chemotherapy was seen overall or within pCR subgroups. Conclusions: Twelve weeks of neoadjuvant nab-pac/carbo is a highly effective anthracycline-free regimen that leads to an excellent pCR-rate of 64% in tumor BRCA1/2-mutated cases. BRC A1/2 mutation status could support this de-escalation strategy in early TNBC, but further prospective validation of survival impacts in larger cohorts and with longer follow up is needed. More detailed survival analyses will be presented at the meeting. Clinical trial information: NCT01815242.

Neoadjuvant talazoparib (TALA) in patients (pts) with germline BRCA1/2 (gBRCA1/2) mutation-positive, early HER2-negative breast cancer (BC): Exploration of tumor BRCA mutational status and zygosity and overall mutational landscape in a phase 2 study.

554 Background: TALA is a poly(ADP-ribose) polymerase inhibitor approved as monotherapy for adult pts with g BRCA1/2-mutated HER2-negative locally advanced/metastatic BC. We report biomarker analyses from a phase 2, nonrandomized, single-arm, open-label study (NEOTALA; NCT03499353) evaluating the efficacy and safety of TALA in the neoadjuvant setting for pts with early g BRCA1/2-mutated HER2− BC. Efficacy and safety results are presented separately. Methods: The biomarker analysis population was all pts treated with TALA for whom biomarker results are available. To support molecular eligibility, blood was tested using BRCAnalysis CDx (Myriad Genetics). Baseline tumor tissue was retrospectively tested using FoundationOne CDx, with BRCA1/2 zygosity assessed using somatic-germline-zygosity (SGZ; Sun et al. JCO PO, 2018). Germline mutational status of 14 non- BRCA DNA damage response (DDR) genes was retrospectively assessed in baseline saliva samples using Ambry CustomNext-Cancer. Mutations were defined as known/likely pathogenic/deleterious variants, including copy number alterations (CNAs). Association between mutational status of MYC or RAD21 and primary endpoint pathological complete response (pCR) as per Independent Central Review was investigated with logistic regression. Results: Of 52 evaluable tumor samples from 61 treated pts, 39 (75%) and 13 (25%) pts exhibited BRCA1 and BRCA2 mutations, respectively; 1 (2%) pt exhibited mutations in both genes, and 1 (2%) pt had mutations in neither. BRCA loss of heterozygosity (LOH) was seen in 42/43 (98%) evaluable BRCA-mutant tumors. Of 45 pts evaluable centrally for both germline and tumor, 44/45 (98%) pts exhibited the same BRCA mutation in tumor as originally detected in germline, with the remaining pt exhibiting a g BRCA1 mutation, but lacking a tumor BRCA mutation. None of 49 saliva-evaluable pts exhibited non- BRCA germline DDR mutations. TP53 (51 [98%] pts) was the most frequently mutated gene in tumors. MYC and RAD21 (each 14 [27%] pts) were the most frequent CNAs. No evidence of association between mutational status of MYC or RAD21 and pCR was found (odds ratio=0.39, 95% CI 0.12-2.30). Based on a cutoff of ≥16%, genomic LOH was elevated in 24/27 (89%) tumors evaluable for both gLOH and pCR, precluding assessment of the potential association of gLOH high/low status with pCR. Conclusions: Tumor BRCA mutations were evident in nearly all pts in the biomarker analysis population, with BRCA LOH evident in all but 1 BRCA-mutated tumor. No pts had non- BRCA germline DDR gene mutations; tumor TP53 mutations were near-universal. MYC and RAD21 each exhibited CNAs in 27% of tumors, with no association with pCR. These results support the central role of BRCA mutations in tumor pathobiology in this indication. Clinical trial information: NCT03499353.

BRCA1 Protein Expression Predicts Survival in Glioblastoma Patients from an NRG Oncology RTOG Cohort

Purpose: Glioblastoma, the most common malignant brain tumor, was associated with a median survival of <1 year in the pre-temozolomide (TMZ) era. Despite advances in molecular and genetic profiling studies identifying several predictive biomarkers, none has been translated into routine clinical use. Our aim was to investigate the prognostic significance of a panel of diverse cellular molecular markers of tumor formation and growth in an annotated glioblastoma tissue microarray (TMA). Methods and Materials: A TMA composed of archived glioblastoma tumors from patients treated with surgery, radiation, and non-TMZ chemother­apy, was provided by RTOG. RAD51, BRCA-1, phosphatase and tensin homolog tumor suppressor gene (PTEN), and miRNA-210 expression levels were assessed using quantitative in situ hybridization and automated quantitative protein analysis. The objectives of this analysis were to determine the association of each biomarker with overall survival (OS), using the Cox proportional hazard model. Event-time distributions were estimated using the Kaplan-Meier method and compared by the log-rank test. Results: A cohort of 66 patients was included in this study. Among the 4 biomarkers assessed, only BRCA1 expression had a statistically significant correlation with survival. From univariate analysis, patients with low BRCA1 protein expression showed a favorable outcome for OS (p = 0.04; hazard ratio = 0.56) in comparison with high expressors, with a median survival time of 18.9 versus 4.8 months. Conclusions: BRCA1 protein expression was an important survival predictor in our cohort of glioblastoma patients. This result may imply that low BRCA1 in the tumor and the consequent low level of DNA repair cause vulnerability of the cancer cells to treatment.

2O Association of RAD51 with homologous recombination deficiency (HRD) and clinical outcomes in untreated triple-negative breast cancer (TNBC): Analysis of the GeparSixto randomized clinical trial

Current genetic and genomic tests that measure HRD show limited predictive value. We compare the performance of a functional HRD test based on scoring RAD51 nuclear foci with genetic/genomic HRD tests, and assess its capacity to select patients (pts) with primary TNBC sensitive to platinum-based neoadjuvant chemotherapy (NACT). A retrospective, blinded analysis from the GeparSixto randomized trial was conducted on TNBC pts who received neoadjuvant paclitaxel plus non-pegylated liposomal doxorubicin (Myocet®) and bevacizumab (PM) or PM plus carboplatin (PMCb). Functional HRD biomarkers (RAD51, BRCA1 and yH2AX nuclear foci) were quantified in formalin-fixed paraffin-embedded (FFPE) tumor samples on a tissue microarray format (TMA). Concordance analyses were performed between the RAD51 score and tumor BRCA (tBRCA) status or genomic HRD score (myChoice® CDx). Associations with clinical outcomes were studied by logistic (pathological complete response, pCR) and Cox (disease-free survival, DFS) regression models. Functional HRD was predefined as a RAD51 score ≤10% (RAD51-low). RAD51, BRCA1 and yH2AX were successfully scored in 133/200 TMA cores (67%). Functional HRD by RAD51-low was evidenced in 81/133 tumors (62%). The RAD51 test identified 93% of tBRCA-mutated tumors and 45% of the non-tBRCA mutant cases as functional HRD. The concordance between RAD51 and genomic HRD was 87% (95%CI 79-93%). In pts with RAD51-high tumors, the pCR rate was similar between treatment arms (PMCb 31% vs PM 39%, odds ratio (OR) 0.71, 0.23-2.24, p=0.561). Pts with RAD51-low tumors benefited from PMCb (66% vs 33%, OR 3.96, 1.56-10.05, p=0.004; interaction test p=0.023). The addition of Cb showed a trend towards better DFS in both RAD51-high (hazard ratio (HR) 0.40, 0.12-1.29, p=0.125) and RAD51-low (HR 0.45, 0.16-1.25, p=0.124) groups. The RAD51 test is highly concordant with tBRCA mutation and genomic HRD. RAD51 independently predicts clinical benefit from adding Cb to NACT in TNBC. Our results support further development to incorporate RAD51-testing in the clinical decision making.

9P BRCA1 promoter methylation confers a more favorable prognosis to systemically untreated young triple-negative breast cancer patients than tumour BRCA1 mutation

The prognoses of systemically treated, triple-negative breast cancer (TNBC) patients with a pathogenic tumor BRCA1 mutation (tBRCA1m) or BRCA1 promoter methylation (BRCA1 PM) have been widely studied. However, the prognosis for systemically untreated women remains unknown. This study investigates the prognosis of systemically untreated young N0 TNBC patients according to tumor BRCA1 status.

Characterisation of PALB2 tumours through whole-exome and whole-transcriptomic analyses

Rare protein-truncating variants (PTVs) in PALB2 confer increased risk to breast cancer, but relatively few studies have reported the characteristics of tumours with PALB2 PTVs. In this study, we describe molecular characteristics of tumours with either germline or somatic alterations in PALB2. DNA from fresh frozen tumour tissues and matched peripheral blood lymphocytes for 560 breast cancer patients was subjected for whole-exome sequencing (WES), and RNA from tumour tissues was subjected to RNA sequencing (RNA-seq). We found six cases with germline and three with somatic protein-truncating variants in PALB2. The characteristics of tumours in patients with PALB2 PTVs were similar to those with BRCA1 and BRCA2 PTVs, having significantly more somatic alterations, and a high proportion of the mutational signature and genomic scar scores characteristic of deficiencies in homologous recombination (HR), compared to tumours arising in non-carriers. Unlike tumours arising in patients with BRCA1 and BRCA2 PTVs, PALB2 tumours did not have high prevalence of TP53 somatic alterations or an enriched immune microenvironment. In summary, PALB2 tumours show the homologous recombination deficiencies characteristic of BRCA1 and BRCA2 tumours, and highlight the potential clinical relevance of PALB2 mutational status in guiding therapeutic choices.

BRCA1 and BRCA2 Tumor Suppressor Function in Meiosis.

Meiosis is a specialized cell cycle that results in the production of haploid gametes for sexual reproduction. During meiosis, homologous chromosomes are connected by chiasmata, the physical manifestation of crossovers. Crossovers are formed by the repair of intentionally induced double strand breaks by homologous recombination and facilitate chromosome alignment on the meiotic spindle and proper chromosome segregation. While it is well established that the tumor suppressors BRCA1 and BRCA2 function in DNA repair and homologous recombination in somatic cells, the functions of BRCA1 and BRCA2 in meiosis have received less attention. Recent studies in both mice and the nematode Caenorhabditis elegans have provided insight into the roles of these tumor suppressors in a number of meiotic processes, revealing both conserved and organism-specific functions. BRCA1 forms an E3 ubiquitin ligase as a heterodimer with BARD1 and appears to have regulatory roles in a number of key meiotic processes. BRCA2 is a very large protein that plays an intimate role in homologous recombination. As women with no indication of cancer but carrying BRCA mutations show decreased ovarian reserve and accumulated oocyte DNA damage, studies in these systems may provide insight into why BRCA mutations impact reproductive success in addition to their established roles in cancer.

Altering the Microbiome Inhibits Tumorigenesis in a Mouse Model of Oviductal High-Grade Serous Carcinoma.

Studies have shown bacteria influence the initiation and progression of cancers arising in sites that harbor rich microbial communities, such as the colon. Little is known about the potential for the microbiome to influence tumorigenesis at sites considered sterile, including the upper female genital tract. The recent identification of distinct bacterial signatures associated with ovarian carcinomas suggests microbiota in the gut, vagina, or elsewhere might contribute to ovarian cancer pathogenesis. Here, we tested whether altering the microbiome affects tumorigenesis in a mouse model of high-grade serous carcinoma (HGSC) based on conditional oviduct-specific inactivation of the Brca1, Trp53, Rb1, and Nf1 tumor suppressor genes. Cohorts of control (n = 20) and antibiotic-treated (n = 23) mice were treated with tamoxifen to induce tumor formation and then monitored for 12 months. The antibiotic cocktail was administered for the first 5 months of the monitoring period in the treatment group. Antibiotic-treated mice had significantly fewer and less advanced tumors than control mice at study endpoint. Antibiotics induced changes in the composition of the intestinal and vaginal microbiota, which were durable in the fecal samples. Clustering analysis showed particular groups of microbiota are associated with the development of HGSC in this model. These findings demonstrate the microbiome influences HGSC pathogenesis in an in vivo model that closely recapitulates the human disease. Because the microbiome can modulate efficacy of cancer chemo- and immunotherapy, our genetically engineered mouse model system may prove useful for testing whether altering the microbiota can improve the heretofore poor response of HGSC to immunotherapies. SIGNIFICANCE: This study provides strong in vivo evidence for a role of the microbiome in ovarian cancer pathogenesis.

Time-resolved single-cell analysis of Brca1 associated mammary tumourigenesis reveals aberrant differentiation of luminal progenitors

It is unclear how genetic aberrations impact the state of nascent tumour cells and their microenvironment. BRCA1 driven triple negative breast cancer (TNBC) has been shown to arise from luminal progenitors yet little is known about how BRCA1 loss-of-function (LOF) and concomitant mutations affect the luminal progenitor cell state. Here we demonstrate how time-resolved single-cell profiling of genetically engineered mouse models before tumour formation can address this challenge. We found that perturbing Brca1/p53 in luminal progenitors induces aberrant alveolar differentiation pre-malignancy accompanied by pro-tumourigenic changes in the immune compartment. Unlike alveolar differentiation during gestation, this process is cell autonomous and characterised by the dysregulation of transcription factors driving alveologenesis. Based on our data we propose a model where Brca1/p53 LOF inadvertently promotes a differentiation program hardwired in luminal progenitors, highlighting the deterministic role of the cell-of-origin and offering a potential explanation for the tissue specificity of BRCA1 tumours.

BRCA2 promotes DNA-RNA hybrid resolution by DDX5 helicase at DNA breaks to facilitate their repair‡.

The BRCA2 tumor suppressor is a DNA double-strand break (DSB) repair factor essential for maintaining genome integrity. BRCA2-deficient cells spontaneously accumulate DNA-RNA hybrids, a known source of genome instability. However, the specific role of BRCA2 on these structures remains poorly understood. Here we identified the DEAD-box RNA helicase DDX5 as a BRCA2-interacting protein. DDX5 associates with DNA-RNA hybrids that form in the vicinity of DSBs, and this association is enhanced by BRCA2. Notably, BRCA2 stimulates the DNA-RNA hybrid-unwinding activity of DDX5 helicase. An impaired BRCA2-DDX5 interaction, as observed in cells expressing the breast cancer variant BRCA2-T207A, reduces the association of DDX5 with DNA-RNA hybrids, decreases the number of RPA foci, and alters the kinetics of appearance of RAD51 foci upon irradiation. Our findings are consistent with DNA-RNA hybrids constituting an impediment for the repair of DSBs by homologous recombination and reveal BRCA2 and DDX5 as active players in their removal.

MiR-21 Plays a Dual Role in Tumor Formation and Cytotoxic Response in Breast Tumors

Simple SummarymiR-21 is an oncogenic microRNA that has been associated with breast tumor growth and metastasis in vitro and is also noted to be upregulated by cytotoxic stressors in model systems and in breast cancer patients who have undergone radiation. In the present study, our findings demonstrate the novel role of miR-21 in vivo for breast cancer initiation and metastases, and in sensitizing tumor cells to cytotoxic therapy by upregulating the FAS/FASL signaling pathway.Breast cancer (BrCa) relies on specific microRNAs to drive disease progression. Oncogenic miR-21 is upregulated in many cancers, including BrCa, and is associated with poor survival and treatment resistance. We sought to determine the role of miR-21 in BrCa tumor initiation, progression and treatment response. In a triple-negative BrCa model, radiation exposure increased miR-21 in both primary tumor and metastases. In vitro, miR-21 knockdown decreased survival in all BrCa subtypes in the presence of radiation. The role of miR-21 in BrCa initiation was evaluated by implanting wild-type miR-21 BrCa cells into genetically engineered mouse models where miR-21 was intact, heterozygous or globally ablated. Tumors were unable to grow in the mammary fat pads of miR-21−/− mice, and grew in ~50% of miR-21+/− and 100% in miR-21+/+ mice. The contribution of miR-21 to progression and metastases was tested by crossing miR-21−/− mice with mice that spontaneously develop BrCa. The global ablation of miR-21 significantly decreased the tumorigenesis and metastases of BrCa, while sensitizing tumors to radio- and chemotherapeutic agents via Fas/FasL-dependent apoptosis. Therefore, targeting miR-21 alone or in combination with various radio or cytotoxic therapies may represent novel and efficacious therapeutic modalities for the future treatment of BrCa patients.

Abstract PS16-25: Comparison of the genetic mutations in sporadic and BRCA1 carrier breast cancer through targeted next generation sequencing

Abstract IntroductionWomen who carry a germline mutation in BRCA1 (breast cancer type 1 susceptibility protein) have an increased risk of developing breast cancer in their lifetimes. Carriers tend to develop breast cancer at a younger age and their tumors are generally aggressive. Although BRCA1 breast cancers have been researched, many questions remain. The purpose of this study was to analyze the mutational landscape of tumors from BRCA1 carriers and compare them to tumors of sporadic breast cancer. MethodsPathology reports were reviewed to identify cases of breast cancer (BC) and the ER/PR/HER2 status was noted as well as the Ki67 proliferation index and patient age. Next generation sequencing (NGS) was performed on 72 BC tumors; 26 from BRCA1 carriers and 46 sporadic BC tumors. Two targeted panels were used for sequencing, the Oncomine Comprehensive Assay by Thermo Fisher Scientific on an Ion Torrent S5 XL sequencer and the AmpliSeq for Illumina Cancer HotSpot Panel. Mutations in a total of 44 cancer associated genes common to both panels were analyzed including TP53, RB1, PTEN, NRAS, ERBB2, PIK3CA, and BRAF. Missense and nonsense single nucleotide variants with a variant allele frequency &amp;gt;3% and coverage &amp;gt;150 reads were considered as well as insertions/deletions. Pathogenicity was determined using ClinVar and Varsome. Mutations were classified as benign, likely benign, variants of uncertain significance, likely pathogenic, and pathogenic.ResultsPathogenic/likely pathogenic variants were identified in 15 genes. TP53 was the most commonly mutated gene with pathogenic/likely pathogenic variants in 13 (50%) BRCA1 carriers’ tumors and 18 (39%) sporadic tumors. Having a TP53 mutation did not increase the likelihood of having other pathogenic mutations in either BRCA1 carriers or sporadic tumors; 74% of all tumors with p53 mutations had no additional pathogenic mutations overall. PIK3CA pathogenic/likely pathogenic mutations were significantly more common in sporadic tumors (26%) than BRCA1 carrier tumors (8%). PIK3CA mutation did not increase the likelihood of other gene mutations and did not correlate with TP53 mutations. BRCA1 pathogenic mutations were identified in four cases with no germline testing and likely represent somatic mutations. No pathogenic mutations were found in 12 (46%) of the BRCA1 carriers’ tumors and 10 (22%) sporadic tumors. There were four BRCA1 carriers with bilateral BCs; two pairs had the same mutations, one pair had different TP53 pathogenic mutations and another pair had different PIK3CA pathogenic mutations. A total of twenty-four cases were triple negative, 13 sporadic and 11 BRCA1 carriers (see table below). As expected, BRCA1 carriers were diagnosed with BC at a younger age with 21 (81%) cases diagnosed at age &amp;lt; 60 years while 22 (48%) of sporadic cases were in this age group. Conclusion TP53 is the most commonly mutated gene in BCs, even though more common in BRCA1 carriers’ tumors; however, they are not required for tumor development as seen in the 57% of cases in our study with normal TP53 (50% of BRCA1 carriers). No specific additional pathogenic mutation was commonly seen in BRCA1 tumors with TP53 mutations. PIK3CA was frequently mutated in sporadic cases and not in BRCA1 carriers. BRCA1 tumors were less likely to have other pathogenic mutations than sporadic tumors in this study of 44 genes. Additional studies will help further elucidate the molecular basis of BRCA1 tumor carcinogenesis. Citation Format: Cynthia Reyes Barron, David Hicks, Xi Wang. Comparison of the genetic mutations in sporadic and BRCA1 carrier breast cancer through targeted next generation sequencing [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS16-25.

Abstract PS8-32: Effects of DNA-damaging and demethylating agents on alternate mRNA splicing in BRCA2

Abstract Introduction DNA sequence variants of unknown clinical significance (VUSs) are routinely identified during genetic testing of BRCA2 and other tumor suppressor genes associated with hereditary breast/ovarian cancer syndrome (HBOC). To determine which VUSs could be classified as pathogenic mutations, sequence variants near intron-exon boundaries are tested for effects on normal splicing patterns. However, these investigations can be complicated by potential genome-wide disruptions of normal splicing patterns caused by therapeutic agents. To test the potential contribution of systemic therapies to alternative splicing events in BRCA2, we have tested the effects of two DNA damaging agents and two demethylating agents on the relative levels of the naturally occurring alternative splicing variant BRCA2Δ3. While the protein product of this alternative splicing event has not been characterized, the BRCA2Δ3 mRNA maintains the full-length translational reading frame, and lacks sequence encoding EMSY and PALB binding domains as well as transactivation function. Previous work has shown that, while some VUSs associated with increased levels of BRCA2Δ3 in lymphoblastoid cell lines are not pathogenic, germline deletions that eliminate BRCA2 exon 3 are associated with increased breast cancer risk. Thus, alternative splicing events that alter relative levels of the BRCA2Δ3 mRNA variant may serve both as an indicator of the effects of some systemic therapies on genome-wide splicing defects and also BRCA2 gene function per se. Methods 1) To determine whether therapeutic DNA damaging agents can alter the levels of Δ3 alternate splicing isoforms, the breast cancer cell line MCF7 was treated with either doxorubicin or bleomycin, and isoform-specific RT-PCR was used to compare relative levels of splice junctions containing or skipping exon 3. 2) To determine whether DNA demethylating agents known to promote expression of some tumor suppressors can alter the levels of Δ3, MCF7 and/or the non-cancer breast cell line MCF 10A was treated with 5-aza 2’-deoxycytidine (5-AzadC) or 5-Azacytidine (5-AzaC), and again isoform-specific RT-PCR was used to compare relative levels of splice junctions containing or skipping exon 3. 3) To determine whether the BRCA2 Δ3 isoform was equally accessible to translational machinery in all cell types, RNA was prepared from separated nuclear and cytoplasmic fractions of MCF7 and MCF 10A and isoform-specific RT-PCR was used to estimate levels of cytoplasmic Δ3 available to translational machinery. Results and conclusions 1) While bleomycin decreases the relative levels of Δ3 compared with untreated controls, doxorubicin increases relative levels of Δ3 in MCF7. This suggests that some DNA damaging agents may cause changes in splicing patterns that may affect therapeutic effectiveness. 2) While both 5-AzaC and 5-AzadC reduce relative levels of Δ3 in MCF7, 5-azadC does not reduce relative levels of Δ3 in MCF 10A, suggesting there may be a cell type-specific splicing response to genomic demethylation therapies. 3) MCF 10A limits the level of Δ3 that can accumulate in the cytoplasm, but this regulatory mechanism is absent from MCF7, indicating there is a cell type-specific mechanism that limits the amount of alternately spliced mRNA variants that are available to translational machinery. Citation Format: James D. Fackenthal, Talia Ishfaq, Zaain Ahmad, Nourhan Mohamed, Milica Janosevic, Ziyad Abdelrahim, Jessica Georgopulos. Effects of DNA-damaging and demethylating agents on alternate mRNA splicing in BRCA2 [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS8-32.

Abstract PS5-06: Prospective testing for PIK3CA/AKT1/PTEN alterations in tumor tissue from 1440 patients with advanced hormone receptor-positive HER2-negative breast cancer (HR+/HER2- BC) or triple-negative breast cancer (TNBC) screened for the IPATunity130 randomized phase 3 trial

Abstract Background The PI3K/AKT signaling pathway plays a significant role in both HR+ BC and TNBC. IPATunity130 is a double-blind, placebo-controlled, randomized phase 3 trial of ipatasertib in combination with paclitaxel in patients with PI3K/AKT1/PTEN-altered HR+ or TNBC. A next-generation sequencing (NGS)-based assay from Foundation Medicine Inc. (FMI) was used to select patients prospectively for enrollment in this trial.Patients and methods An investigational clinical trial assay (CTA) of a composite 3-gene biomarker signature [Kim, Lancet Oncol 2017] based on the FoundationOne® CDx assay was used to identify patients with PI3K/AKT pathway-activated tumors as eligible for enrollment in IPATunity130 (NCT03337724). Qualifying alterations for the 3-gene signature (referred to as ‘biomarker-positive’) comprised activating mutations in PIK3CA and/or AKT1, and/or loss of function (LOF) alterations in PTEN represented by homozygous or heterozygous deletions, dominant-negative mutations, or inactivating mutations under loss of heterozygosity. Study sites were required to submit formalin-fixed paraffin-embedded archival or fresh biopsy tissue derived from primary or metastatic tumors for patient screening. IPATunity130 includes three independent cohorts: Cohort A (biomarker-positive TNBC); Cohort B (biomarker-positive HR+/HER2– BC); and Cohort C (biomarker-negative TNBC). Results In total, 1736 patients were screened, from whom 1690 samples were tested by FMI. Of these, 1475 (87%) produced a valid NGS result. The remaining 215 (13%) failed quality control for reasons including insufficient tissue, DNA yield, lab error, and computational failure. Alteration status for PIK3CA and/or AKT1 and/or PTEN was positive in 703 (49%) of 1440 CTA-evaluable samples. In the HR+/HER2– cohort, the breakdown of CTA-positive samples was 301/356 (85%) PIK3CA/AKT1 mutations and 86/356 (24%) PTEN LOF alterations. In TNBC, 183/347 (53%) had PIK3CA/AKT1 mutations and 193/347 (56%) had PTEN LOF alterations. CTA results according to baseline characteristics are shown overall and by subtype below. The most common mutations detected outside the 3-gene biomarker signature in the screened population were in the TP53, BRCA1, RB1, BRCA2, and NF1 genes in the TNBC cohort and the TP53, GATA3, CDH1, MAP3K1, and ESR1 genes in the HR+/HER2– cohort. In the HR+/HER2– cohort, 30 (14%) of 213 metastatic tumors had ESR1 mutations compared with 10/414 (2%) primary tumors. Tumor BRCA1 mutations were more common in patients aged ≤50 years whereas MAP3K1 mutations were more common in those aged &amp;gt;50 years.Conclusions IPATunity130 is the first reported pivotal trial to utilize the 3-gene biomarker CTA in HR+/HER2– BC and TNBC to screen for patients with PI3K/AKT pathway-activated tumors. The 3-gene biomarker CTA detected alterations in 49% of screened patients, with a higher prevalence of PIK3CA/AKT1/PTEN alterations in HR+/HER2– BC than TNBC. Additional analyses are planned to assess correlations between clinical outcomes and tumor characteristics. SubgroupPIK3CA/AKT1/PTEN alteration, n/N (%)OverallHR+/HER2–TNBCAll patient samples703/1440 (49)356/647 (55)347/793 (44)Age, years≤50219/475 (46)99/195 (51)120/280 (43)&amp;gt;50484/965 (50)257/452 (57)227/513 (44)Sample sourcePrimary456/941 (48)232/414 (56)224/527 (43)Metastatic222/448 (50)112/213 (53)110/235 (47)Geographic regionNorth America60/102 (59)33/49 (67)27/53 (51)Asia-Pacific172/330 (52)81/145 (56)91/185 (49)Europe301/633 (48)171/310 (55)130/323 (40)Rest of world170/375 (45)71/143 (50)99/232 (43) Citation Format: Heidi Savage, Wendy Lin, Mafalda Oliveira, Carlos Barrios, Joyce O’Shaughnessy, Nicholas Turner, Rebecca Dent, Steven J Isakoff, Shigehira Saji, Qinshu Lian, Denise Bradley, Sarah-Jayne Reilly, Heather Hinton, Matthew J Wongchenko, Aruna Mani, Sung-Bae Kim. Prospective testing for PIK3CA/AKT1/PTEN alterations in tumor tissue from 1440 patients with advanced hormone receptor-positive HER2-negative breast cancer (HR+/HER2- BC) or triple-negative breast cancer (TNBC) screened for the IPATunity130 randomized phase 3 trial [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS5-06.