Background: Ovarian cancer is one of the most common hereditary cancers in women. Mutations in the BRCA1 gene increase a woman's risk of ovarian cancer. Testing for BRCA1 mutations is cumbersome and impractical for large populations. Therefore, we developed an efficient strategy to detect various types of BRCA1 dysfunction and also determined the relative frequency of BRCA1 dysfunction in ovarian cancer.
Methods: Tumors from 221 patients with epithelial ovarian cancer were screened for loss of heterozygosity (LOH) at the BRCA1 locus. BRCA1 complementary DNA (cDNA) and genomic DNA from all cancers with BRCA1 LOH (106 tumors) or noninformative status (15 tumors) were polymerase chain reaction (PCR) amplified and analyzed for protein truncation in a coupled transcription/translation test. When truncated BRCA1 protein was detected, the BRCA1 gene from both the tumor and a paired blood sample was sequenced. When BRCA1 expression in tumor cDNA was not detected with a protein truncation test, a methylation-specific PCR was used to determine whether the promoter region of BRCA1 was methylated and thus inactivated. All statistical tests were two-sided.
Results: Fifty-one (23.1%) of 221 tumors had BRCA1 dysfunction, including 18 with germline mutations, 15 with somatic mutations, and 18 with monoallelic or biallelic hypermethylated promoters. By the consideration of only tumors with LOH or that were noninformative, the efficiency for detecting BRCA1 dysfunction improved to 45 (37.2%) of 121 tumors. Therefore, LOH/noninformative was a strong predictor of mutation status (Fisher's exact test, P<.001). However, this subset of tumors did not include those with BRCA1 missense mutations (estimated at six [2.7%] of 221 not detected by our method) or biallelic promoter methylation (estimated at six [2.7%] of 221).
Conclusions: BRCA1 dysfunction in ovarian cancer is common and occurs via multiple mechanisms. The use of LOH, rather than a family history of ovarian cancer, as a first step in a screening strategy, followed by protein truncation testing, appears to increase the chance of identifying tumors with BRCA1 dysfunction.