ESR1 and breast cancer: This cohort also offered an opportunity to study patient willingness to continue ET beyond 5 years, because beginning in 2005, patients with estrogen receptor (ER)–positive, human epidermal growth factor receptor (HER2)–negative early-stage breast cancer at MDA were offered extended adjuvant ET, after the initial trial results of MA.17.11,12 A secondary aim was to examine how patients’ reasons for discontinuation evolve over time.