BRCA1 and breast cancer: For first breast cancers, the average age of onset in the BRCA1- and BRCA2-positive groups (90 and 98 cases) and BRCA-negative group (588 cases) was 40.2 years (95% confidence interval (CI) 38.15–42.25), 41.7 years (95% CI 39.71–43.70), and 45.4 years (95% CI 44.54–46.26), respectively.