CHEK2 and breast cancer: Furthermore, LOH affecting the CHEK2 locus was present in 41% (n = 302) of 736 TCGA BCs affecting patients who lacked a CHEK2 germline variant, a frequency similar to that of CHEK2 LOH in BC patients with the low-risk CHEK2 p.Ile157Thr germline variant (P = .46, Mann-Whitney U test) but statistically significantly lower than that observed in high-risk–variant CHEK2-associated BCs (P = .002, Mann-Whitney U test; Figure 2A).