Patients aged 80 years or older were 51%, 47% and 36% less likely to be treated with adjuvant radiotherapy for stage I (RR = 0.49; 95% CI: 0.43, 0.56), stage II (RR = 0.53; 95% CI: 0.43, 0.64), and stage III (RR = 0.64; 95% CI: 0.34, 1.05) cancers, respectively, compared to those less than 50 years of age, adjusting for age at diagnosis, year of diagnosis, ER/PR status and hormone therapy, neo-adjuvant chemotherapy and adjuvant chemotherapy. This evidence concerns the gene ESR1 and cancer.