Characteristics of BRCA1 mutations in a population-based case series of breast and ovarian cancer.

Breast and ovarian cancers account for approximately 210000 newly diagnosed cases per year. More than half a million American women are estimated to be carriers of a breast cancer susceptibility gene. The purpose of this study was to assess the association of characteristics such as, age at diagnosis, race/ethnicity and family history of cancer with inherited BRCA1 mutations in a population-based sample of breast and ovarian cancer cases. No selection was made by race, age at diagnosis or positive family history of breast or ovarian cancer. The population under study was all breast cancer cases diagnosed in Orange County, CA, during the 1-year period beginning 1 March 1994 and all ovarian cancer cases diagnosed in Orange County during the 2-year period beginning 1 March 1994. This report focuses on the first consecutively ascertained 802 participating probands enrolled in the study, of which 9 were male breast cancer probands, 673 were female breast cancer probands and 120 were ovarian cancer probands. We observed 11 BRCA1 mutations or 1.6% (95% CI: 0.8-2.9) among the 673 female breast cancer probands and 4 BRCA1 mutations or 3.3% (95% CI: 0.8-8. 3) among the 120 ovarian cancer probands. No BRCA1 mutations were identified among the 98 non-white breast and ovarian cancer probands. The prevalence of BRCA1 mutations in non-Hispanic-white breast cancer cases below the age of 50 years was 2%. Positive family history of breast or ovarian cancers was significantly associated with BRCA1 mutation status among breast cancer probands. Similarly, positive family history of breast or ovarian cancer was significantly associated with BRCA1 mutation status among the ovarian cancer probands. In summary, we present results on the prevalence of BRCA1 mutations in a significantly larger sample of population-based breast and ovarian cancer cases than previously reported. The results indicate that, using a conservative approach to targeted genotyping of BRCA1, the frequency of mutations was consistent with those reported using similar methods of population-based case ascertainment.