Alison Meynert

Structural Variants at the BRCA1/2 Loci are a Common Source of Homologous Repair Deficiency in High-grade Serous Ovarian Carcinoma

Abstract Purpose: The abundance and effects of structural variation at BRCA1/2 in tumors are not well understood. In particular, the impact of these events on homologous recombination repair deficiency (HRD) has yet to be demonstrated. Experimental Design: Exploiting a large collection of whole-genome sequencing data from high-grade serous ovarian carcinoma (N = 205) together with matched RNA sequencing for the majority of tumors (N = 150), we have comprehensively characterized mutation and expression at BRCA1/2. Results: In addition to the known spectrum of short somatic mutations (SSM), we discovered that multi-megabase structural variants (SV) were a frequent, unappreciated source of BRCA1/2 disruption in these tumors, and we found a genome-wide enrichment for large deletions at the BRCA1/2 loci across the cohort. These SVs independently affected a substantial proportion of patients (16%) in addition to those affected by SSMs (24%), conferring HRD and impacting patient survival. We also detail compound deficiencies involving SSMs and SVs at both loci, demonstrating that the strongest risk of HRD emerges from combined SVs at both BRCA1 and BRCA2 in the absence of SSMs. Furthermore, these SVs are abundant and disruptive in other cancer types. Conclusions: These results extend our understanding of the mutational landscape underlying HRD, increase the number of patients predicted to benefit from therapies exploiting HRD, and suggest there is currently untapped potential in SV detection for patient stratification.

Multiomic Characterization of High-Grade Serous Ovarian Carcinoma Enables High-Resolution Patient Stratification

Abstract Purpose: High-grade serous ovarian carcinoma (HGSOC) is the most common ovarian cancer type; most patients experience disease recurrence that accumulates chemoresistance, leading to treatment failure. Genomic and transcriptomic features have been associated with differential outcome and treatment response. However, the relationship between events at the gene sequence, copy number, and gene-expression levels remains poorly defined. Experimental Design: We perform multiomic characterization of a large HGSOC cohort (n = 362) with detailed clinical annotation to interrogate the relationship between patient subgroups defined by specific molecular events. Results: BRCA2-mutant (BRCA2m) and EMSY-overexpressing cases demonstrated prolonged survival [multivariable hazard ratios (HR) 0.40 and 0.51] and significantly higher first- and second-line chemotherapy response rate. CCNE1-gained (CCNE1g) cases demonstrated underrepresentation of FIGO stage IV cases, with shorter survival but no significant difference in treatment response. We demonstrate marked overlap between the TCGA- and Tothill-derived subtypes. IMR/C2 cases displayed higher BRCA1/2m frequency (25.5%, 32.5%) and significantly greater immune cell infiltration, whereas PRO/C5 cases had the highest CCNE1g rate (23.9%, 22.2%) and were uniformly low in immune cell infiltration. The survival benefit for cases with aberrations in homologous recombination repair (HRR) genes was apparent across all transcriptomic subtypes (HR range, 0.48–0.68). There was significant co-occurrence of RB loss and HRR gene aberrations; RB loss was further associated with favorable survival within HRR-aberrant cases (multivariable HR, 0.50). Conclusions: These data paint a high-resolution picture of the molecular landscape in HGSOC, better defining patients who may benefit most from specific molecular therapeutics and highlighting those for whom novel treatment strategies are needed to improve outcomes.

Somatic BRCA1/2 mutations are associated with a similar survival advantage to their germline counterparts in tubo-ovarian high grade serous carcinoma

Half of high grade serous tubo-ovarian carcinomas (HGSOC) demonstrate homologous recombination repair (HRR) deficiency, most commonly through germline or somatic pathogenic variants in BRCA1/2 (gBRCA1/2 or sBRCA1/2). gBRCA1/2 is associated with favourable survival, greater response rate to platinum-based chemotherapy, and marked sensitivity to poly(ADP-ribose) polymerase (PARP) inhibitors. sBRCA1/2 has been assumed to confer a similar clinical phenotype; however, few studies have specifically investigated sBRCA1/2 versus gBRCA1/2 to demonstrate their equivalence. We investigated the association of gBRCA1/2, sBRCA1/2 and non-BRCA HRR gene mutations with HGSOC patient survival using two patient cohorts (cohort 1, n = 174 matched FFPE tumour and normal with panel-based sequencing; cohort 2, n = 279 matched fresh tumour and normal with whole genome sequencing). TCGA-OV samples (n = 316) were used for external validation. Patients with HRR-mutant tumours (BRCA1, BRCA2, non-BRCA HRR-mutant) demonstrated prolonged survival across both cohorts (cohort 1: multivariable hazard ratio [multiHR] 0.53 [0.32-0.87]; cohort 2: multiHR 0.36 [0.25-0.51]). gBRCA1/2 and sBRCA1/2 were associated with a similar survival benefit compared to the HRR-wildtype group in the combined cohort (cohort 1 +2) (gBRCA1/2: multiHR 0.50 [0.34-0.71]; sBRCA1/2: multiHR 0.41 [0.25-0.68]). These findings were recapitulated using the TCGA-OV dataset (gBRCA1/2: multiHR 0.56 [0.34-0.91]; sBRCA1/2: multiHR 0.48 [0.25-0.92]). Non-BRCA HRR mutations were associated with marked survival advantage (multiHR vs HRR-wildtype 0.22 [0.11-0.45]). The survival advantage in BRCA1-mutant cases (germline or somatic) was less marked (multiHR for non-BRCA HRR-mutant vs BRCA1-mutant 0.41 [0.19-0.90]). gBRCA1/2, sBRCA1/2 and non-BRCA HRR mutations were all associated with high HRDetect scores measuring HRR deficiency (median 1.00 versus 0.56 in HRR-wildtype, P < 0.01). gBRCA1/2 and sBRCA1/2 are equivalent in their association with prolonged survival. Non-BRCA HRR gene mutations may be associated with markedly favourable survival in HGSOC.