A high prevalence of BRCA1 mutations among breast cancer patients from the Bahamas.

The Bahamas is a group of islands in the Caribbean with a high incidence of early onset breast cancer. In isolated populations, the identification of founder mutations in cancer predisposing genes may facilitate genetic testing and counseling. To date, six distinct BRCA1 mutations have been found in patients from cancer families from the Bahamas. The frequencies of these mutant alleles have not been measured in a large series of unselected breast cancer patients from Bahamas. We studied 214 Bahamian women with invasive breast cancer, unselected for age or family history of cancer. All patients were screened for six mutations in the BRCA1 gene that have previously been reported in cancer patients from the Bahamas. A mutation was identified in 49 of the 214 breast cancer patients (23%). The mutation frequency was particularly high in women diagnosed before age 50 (33%) in women with a first-degree relative with breast or ovarian cancer (41%) and in women with bilateral breast cancer (58%). Approximately 23% of unselected cases of breast cancer in the Bahamian population are attributable to a founder mutation in the BRCA1 gene-this is the highest reported mutation prevalence for any country studied to date. Genetic testing for these mutations is advisable for all women diagnosed with breast cancer in the Bahamas.