ESR1 and breast cancer: In a national United Kingdom retrospective study of patients aged ≥ 75 years with ER+/HER2− advanced breast cancer receiving 1L palbociclib plus AI (N = 276), 12- and 24-month rwPFS rates were 75.9% and 64.9%, respectively, and OS rates were 85.1% and 74.0%, respectively (31).