An Early Breast Cancer Trialists' Collaborative Group (EBCTCG) meta-analysis from 1998 comparing adjuvant tamoxifen versus no tamoxifen in patients with estrogen receptor–positive (ER+) or ER-unknown disease identified reductions in the recurrence rate and improvements in survival for patients who received 5 years of tamoxifen versus 1 or 2 years (2). The gene discussed is ESR1; the disease is breast cancer.