Abstract A05: BRCA1 promoter hypermethylation loss in recurrent high-grade serous carcinoma.

Abstract

Abstract Objective: BRCA1 germline mutations are associated with improved ovarian cancer survival, yet secondary revertant mutations that impair chemo-sensitivity can develop after platinum-based therapy. BRCA1 promoter hypermethylation, present in ~10% of all high-grade serous carcinomas (HGSCs), is associated with reduced gene and protein expression. We hypothesize that BRCA1 promoter hypermethylation decreases in recurrent HGSCs compared with matched primary samples. Methods: Primary, untreated HGSCs with known BRCA1 promoter methylation status and matched recurrent samples were macrodissected from archival slides. After DNA was extracted and bisulfite treated, pyrosequencing was performed across 11 CpG sites within the BRCA1 promoter to quantify methylation using a CLIA-approved assay. The methylation percentage was calculated from allele frequencies and 10% or greater is considered hypermethylated. Validation data were obtained from The Cancer Genome Atlas (TCGA) substudy of paired primary and recurrent HGSCs. Results: Eleven patients with matched primary and recurrent tumors were evaluated. Six patients had hypermethylated primary tumors, with methylation percentages ranging from 35-69%. We found that BRCA1 promoter methylation decreased 16-95% in five recurrent samples compared to their primary tumors. One patient with a demethylated recurrent tumor had platinum refractory disease clinically and died 12 months after diagnosis. In contrast, the only patient with an increase (74%) in promoter methylation between primary and recurrent specimens is a long-term survivor alive with disease 14 years after diagnosis. There was negligible change in promoter methylation between primary and recurrent cases for the five unmethylated samples. Three of 17 paired samples from the ovarian TCGA substudy had BRCA1 promoter hypermethylation and showed a 20-50% decrease between primary and recurrent samples with a corresponding increase in BRCA1 gene expression. Conclusion: BRCA1 promoter hypermethylation generally decreases between primary and recurrent HGSCs and can be associated with remarkable clinical outcomes. BRCA1 promoter methylation may be a marker of platinum response in the recurrent disease setting and can be assessed in prospective clinical trials. In addition to BRCA1 somatic revertant mutations, loss of BRCA1 promoter methylation may be another mechanism to restore BRCA1 function in recurrent disease. Citation Format: Maria Bisogna, Fanny Dao, Narciso Olvera, Ruben Bacares, Liying Zhang, Douglas A. Levine. BRCA1 promoter hypermethylation loss in recurrent high-grade serous carcinoma. [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 A05.