ESR1 and breast cancer: The PRIME I and PRIME II multicentre randomized controlled trials demonstrated that women aged 65 years and older, with early-stage breast cancer (axillary node-negative, T0-2, N0-1, M0 for PRIME I and ER expressed, axillary node-negative, T1-T2 for PRIME II) who have undergone lumpectomy, have low recurrence rates, as long as they are compliant with five years of anti-estrogen therapy [3-4].