A large study evaluating CHEK2 mutations in breast cancer patients from Poland found that CHEK2 carriers were significantly more likely to have ER+ (OR = 3.9; 95% CI = 2.7–5.4) than ER- (OR = 2.1; 95% CI = 1.3–3.3) tumors [56]. Here, ESR1 is linked to breast cancer.