Proliferation pathway aberration frequencies in BRCA1- and BRCA2-mutated ovarian cancers.

Abstract

5074 Background: Large-scale genomic analyses of high-grade, advanced-stage serous ovarian cancers by The Cancer Genome Atlas (TCGA) project revealed aberrations in genes comprising key proliferation and survival pathways (RB-E2F, RAS, PI3K) in the majority of tumors. Patients with germline BRCA1/2-mutations have more favorable prognoses than non-BRCA carriers, and recent work suggests that BRCA2 carriers do better than BRCA1. We hypothesized that concurrent proliferation pathway aberrations and BRCA1/2 mutations in tumors might play a role in patient outcome. Methods: Mutation, copy number, and clinical data for 309 TCGA-profiled serous ovarian tumors were downloaded from the MSKCC cBIO web portal. Each tumor was scored as aberrant for a pathway if any gene (RB: RB1, CDKN2A, CCND1, CCND2, E2F3, CCNE1; PI3K: PIK3CA, PTEN, AKT1, AKT2; RAS: KRAS, BRAF, NF1) in that pathway was mutated, amplified, or deleted. Results: 205 of 309 tumors had an aberration in at least one of these pathways. The frequency of pathway alteration differed significantly in BRCA1 (82%, 28/34), BRCA2 (52%, 17/33) and BRCA1/2 WT (66%, 160/242) tumors (BRCA1 vs. BRCA2: Fisher’s p= 0.0096). BRCA1 tumors more frequently contained alterations in multiple pathways than BRCA2 or WT tumors (41% vs. 24% or 25%, respectively). RB-E2F pathway alteration frequency was significantly different (BRCA1: 56%, BRCA2: 18%, WT: 43%, p=0.0043), but no significant differences in PI3K and RAS pathway aberration frequencies (BRCA1%: 41, 38; BRCA2%: 36, 27; WT% 28, 27), respectively, were observed. In agreement with the previous report, BRCA2 patients had significantly better overall survival (OS) than either BRCA1 or WT patients (median OS months for BRCA1: 35.9, BRCA2 45.4, BRCA1/2 WT 27.8; p=0.001). Presence of pathway alterations was not significantly associated with OS in BRCA1, BRCA2, or WT patients in this cohort. Conclusions: These results show a negative association between BRCA2 mutations and aberrations in key proliferation and survival pathways. Beyond BRCA1 and BRCA2 genetic mutations, the elevated frequency of pathway alteration in BRCA1 vs. BRCA2 tumors highlights differences that may be important for patient prognosis as well as therapy responses.