Twenty-year tamoxifen therapy benefit by clinical marker score. Multivariable Cox proportional hazards regression analysis of the 20-year distant recurrence-free interval for premenopausal and postmenopausal breast cancer patients with estrogen receptor–positive and HER2-negative tumors, comparing patients randomly assigned to tamoxifen vs no endocrine therapy (control). Analyses in premenopausal patients adjusted for age, random assignment year, and type of surgery, and analyses in postmenopausal patients adjusted for age, random assignment year, type of surgery, chemotherapy, and radiotherapy. Bold indicates a statistically significant P value less than .05. aHR = adjusted hazard ratio; CI = confidence interval; CMS = clinical marker score; DR = distant recurrence; Ref = referent.