Recently, the final results of the GIM4 phase 3 trial [2] showed that at a median follow-up of more than 12 years, disease-free survival (DFS) and overall survival (OS) outcomes were significantly improved in postmenopausal patients with ER-positive BC who, after adjuvant tamoxifen for 2–3 years, received 5 years of letrozole extension compared to the standard 2–3 years of letrozole (hazard ratios (HRs), 0.78; 95% confidence interval (CI), 0.65–0.93 and 0.77; 0·60–0.98, respectively). The gene discussed is ESR1; the disease is breast cancer.