CHEK2 and breast cancer: The most frequently mutated genes were CHEK2 (n = 12; 2% of the total cohort, 13% of the positive cohort), ATM (n = 9; 1.5% of the total cohort, 10% of the positive cohort) and PALB2 (n = 4; 0.6% of the total cohort, 4.5% of the positive cohort), mostly in families with BC only.