The protein-truncating variant 1100delC (p. Thr367fs, rs555607708r) raises BC risk by two to three times in general risk [74], with 0.2–1.6% of Northern and Eastern Europeans harbouring this mutation, known as CHEK2 PV (Pathogenic variant) [75–77], while FBC cases were 4.8-fold [78].The 1100delC mutation has been specifically associated with ER-positive BC [74]. Here, CHEK2 is linked to breast cancer.