CHEK2 and breast cancer: Different CHEK2 variants have been described, and in the Netherlands, the prevalence of the CHEK2 1100delC variant is relatively high, while other CHEK2 variants (IVS2 + 1G > A, del5395, 1157T) are very rare (The CHEK2 Breast Cancer Case Control Consortium 2004; Hollestelle et al. 2010; Meijers-Heijboer et al. 2002).