Twenty-year tamoxifen therapy benefit by clinically used tumor characteristics. 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). Adjusted for age, random assignment year, tumor size, tumor grade, lymph node status, progesterone receptor status, Ki-67 status, type of surgery, chemotherapy, and radiotherapy. Bold indicates a significant P value less than .05. aHR = adjusted hazard ratio; CI = confidence interval; DR = distant recurrence; PR = progesterone receptor; Ref = referent.