Abstract A07: Homologous recombination mutations and overall survival in high-grade serous, endometrioid, and clear cell ovarian carcinomas.

Background: Defects in homologous recombination (HR) DNA repair are common in high grade serous ovarian, peritoneal and fallopian tube carcinoma (HGSOC). Other than mutations in BRCA1 and BRCA2 (BRCA1/2), the molecular causes of HR deficiency have not been well delineated. The frequency of HR deficiency in non-serous ovarian carcinoma is not known. We previously identified that germline and somatic HR mutations in 13 genes in OC was associated with improved survival. We sought to replicate these data in an independent tumor set, while sequencing a larger number of DNA repair genes. Methods: We used BROCA-HR to sequence 65 DNA repair genes in germline (blood) and tumor DNA from 363 women with ovarian (262), peritoneal (91), or fallopian tube (10) carcinoma from an institutional tissue bank. Cox proportional hazards models, adjusted for stage and residual tumor after cytoreduction, were used to assess associations between mutations in DNA repair genes in HR or related pathways and overall survival from diagnosis. Results: In total, 96/363 (25%) patients had 59 germline and 45 somatic deleterious mutations in HR genes, including 34 germline and 22 somatic BRCA1/2 mutations. Damaging mutations found in other HR genes included 25 germline and 23 somatic in the following genes: 5 ATM, 6 ATR, 1 BAP1, 2 BARD1, 6 BLM, 2 BRIP1, 2 BRE, 1 BRCC3, 2 CHEK2, 1 ERCC1, 1 FANCG, 1 FANCI, 2 FANCL, 8 FANCM, 1 NBN, 2 PALB2, 1 RAD51D, 1 RBBP8, 1 SLX4, 1 UIMC1 and 1 XRCC2. Of 322 HGSOC, HR mutations occurred in 86 patients (26.7%) including 54 (16.8%) germline and 32 somatic (9.9%). HR mutation rates were similar across the different non-serous histologies. Of 13 clear cell OC, 2 (15.3%) had germline mutations in non-BRCA1/2 HR genes and 3 (23.1%) had PTEN/PIK3CA mutations. Of 27 endometrioid OC, 3 (11.1%) had HR mutations (1 germline BRCA1, and 2 non-BRCA1/2 somatic HR mutations). PTEN/PIK3CA mutations were identified in 9 (2.8%) HGSOC, 3 (23.1%) clear cell and 2 (7.5%) endometrioid. HR mutations demonstrated a trend towards improved long-term overall survival (hazard ratio = 0.78, 96% CI 0.57-1.05) after accounting for stage and debulking status. Conclusions: These data not only indicate that damaging HR mutations, both germline and somatic, are found in endometrioid and clear cell as well as HGSOC, but also confirm our previous results showing an association between HR mutations and improved overall survival in OC. We are now sequencing 163 additional non-serous OC to augment the current analysis and these data will be available at presentation. Citation Format: Maria I. Harrell, Matthew J. Maurer, Ethan P. Heinzen, Ming K. Lee, Kimberly R. Kalli, Kathy J. Agnew, Ann L. Oberg, Tom Walsh, Barbara M. Norquist, Lynn C. Hartmann, Scott H. Kaufmann, Elizabeth M. Swisher. Homologous recombination mutations and overall survival in high-grade serous, endometrioid, and clear cell ovarian carcinomas. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr A07.