ESR1 and breast cancer: Phase 1a/1b EMBER (ClinicalTrials.gov identifier: NCT04188548) is a comprehensive, open-label, dose-escalation (phase 1a) trial of imlunestrant followed by several dose-expansion cohorts (phase 1b) examining imlunestrant as monotherapy and in combination with abemaciclib with or without aromatase inhibitors everolimus or alpelisib in ER+ advanced breast cancer and endometrial endometrioid cancer.