Prevalence of founder BRCA1 and BRCA2 mutations in unselected French Canadian women with breast cancer

The frequency of BRCA1 and BRCA2 mutations in women with breast cancer vari es according to the age at diagnosis, family history of cancer, and ethnici ty/country of origin. We set out to estimate the frequency of seven previou sly described founder mutations in BRCA1 and BRCA2 in all eligible French C anadian women diagnosed with invasive breast cancer at one Montreal hospita l over a 20-month period. One hundred and ninety-two patients were eligible and 127 (66.2%) provided blood for genetic testing. We identified 4 women who carried a founder mutation (3.1%, 95% confidence interval 0.9-7.9%) in this population. Interestingly, all the mutations were in BRCA2. The mean a ge at diagnosis for mutation carriers was 51.2 years (range 49.1-53.5). Two of these 4 cases were lobular invasive carcinomas and 2 were ductal carcin omas, histological grade 1 or 2. Despite a small tumor size (less than or e qual to 20 mm), axillary nodal involvement was present in 3 women. Estrogen receptors were strongly expressed in all cases. Two of the 4 cases reporte d a strong family history of breast cancer, but a family history of site-sp ecific breast cancer was a relatively poor indicator of the presence of BRC A2 mutations. The absence of BRCA1 mutations may be a result of chance, but may also reflect different geographical origins of the most common BRCA1 m utations within the French Canadian population.