The mutational spectrum of breast and ovarian tumors from BRCA1 and BRCA2 mutation carriers.
1510 Background: Individuals who carry one mutated copy of the BRCA1 or BRCA2 genes have elevated lifetime risks of breast and ovarian cancer. A number of studies have investigated the somatic mutational spectra of breast and ovarian tumors; however, BRCA1/2mutated tumors are underrepresented. Methods: Sixty-eight formalin-fixed paraffin embedded samples from BRCA1/2patients have been identified. Massively parallel sequencing using 48 gene capture is in process, whole exome sequencing of tumor and matched germline DNA is planned. Data are analyzed using a custom bioinformatics pipeline. Results: In analysis of data from the first 26 breast (4 BRCA1, 6 BRCA2) and ovarian (8 BRCA1, 8 BRCA2) tumors, the majority (23/26, 88%) had 0-2 variants in 48 cancer genes. Known deleterious TP53 mutations were the only variants identified in 2/4 BRCA1 and 2/6 BRCA2 breast tumors. Of those remaining, 2 BRCA1 and 1 BRCA2 breast tumors had no identified deleterious mutations. Two BRCA2 breast tumors with no TP53 mutations had known deleterious mutations in a single gene each - FGFR2 and PI3KCA. One BRCA2 breast tumor with no TP53 mutation had a variant of uncertain significance in FLT3. Finally, one BRCA2 breast tumor had a very high mutational rate, with one deleterious TP53 mutation and 7 other small deletion and single nucleotide variants. For the ovarian tumors, 15/16 BRCA1 and BRCA2 tumors had known deleterious TP53 mutations; the ovarian tumor with no TP53 mutation had no other variants. TP53 mutations were the sole identified mutations in 8 ovarian tumors. One ovarian tumor carried a known JAK3 activating mutation and 4 ovarian tumors carried one variant of uncertain significance in a single gene - SMO, PDGFRA, GNA11 and NRAS. Finally, two ovarian tumors were found to have high mutational rates. Conclusions: Using a targeted resequencing panel, we confirmed the high rate of TP53 mutations in BRCA1/2 breast tumors and observed a higher than expected rate in BRCA1/2 ovarian tumors. Importantly, we have identified mutations in other known driver genes using FFPE samples, allowing generalizability to other sites. These analyses may uncover novel mutations that could be exploited in the development of targeted therapeutic agents for BRCA1/2 carriers.