Meta-analyses indicate that a BRCA1 mutation carries a 47–66% probability of developing breast cancer and a 35–46% probability of developing ovarian cancer over a woman’s lifetime and with a BRCA2 mutation, it is 40–57% for breast and 13–23% for ovarian cancer [16].There is wide differences in BRCA1/2 mutation penetrance estimates between individual studies. This evidence concerns the gene BRCA1 and breast cancer.