CHEK2 and breast cancer: Interestingly, CHEK2, a gene previously reported to impact BC risk via rare and highly penetrant mutations, was identified to be conditionally significant for ER + BC (Table 3); moreover, the SNPs used in CHEK2 expression prediction models generally had little to no correlation with other GWAS index SNPs at the same 22q12.1-q12.2 locus (Table S6 in Additional file 1).