The current National Comprehensive Cancer Network guidelines (NCCN V 3.2013) recommends 10 years of tamoxifen for invasive hormone receptor–positive breast cancer in premenopausal woman or 5 years of tamoxifen and 5 years of an aromatase inhibitor if she experiences menopause during treatment (http://www.nccn.org/professionals/physician_gls/pdf/breast.pdf, accessed 4/9/2014). Here, CYP19A1 is linked to breast cancer.