In 2017, a meta-analysis of 15 studies of breast cancer in Asia (total of 1794 individuals) revealed an association of the rs1065852 *10/*10 (TT) polymorphism in the CYP2D6 gene with worse disease-free survival and relapse in women receiving adjuvant treatment with tamoxifen dosage of 20 mg/day [7]. This evidence concerns the gene CYP2D6 and breast cancer.