In one study of FCs, the frequency of CHEK2 (NM_007194.4): c.1100del; p.Thr367MetfsTer15, was 2% in BC families with at least two or more BC cases diagnosed before the age of 65 years, which is lower but comparable to the 3.7% carrier frequency reported in BC families from the general population [45] (p = 0.7 using Fisher’s exact test). This evidence concerns the gene CHEK2 and breast cancer.