BRCA2 and breast cancer: Therefore, approximately 0.01–0.05% (i.e., 1:10000 - 1:2000) of BC patients, 0.03 – 0.15% (i.e., 1:3333-1:667) of OC patients, and 0.05–0.25% (i.e., 1:2000 - 1:400) of women with HOBC have both parents carrying BRCA1 or BRCA2 mutation.