Although, currently is less common to prescribe 5 or 10 years of tamoxifen treatment for hormone receptor positive postmenopausal BC women with due to other preferred treatment strategies including aromatase inhibitors for 5 or more years, switch therapies with both aromatase inhibitors and tamoxifen, there are some premenopausal patients that are still candidates for tamoxifen treatment and also it is important to take in account that in basic resources settings tamoxifen is still the first choice of treatment in both pre and postmenopausal women.49, 50. The gene discussed is CYP19A1; the disease is breast cancer.