ESR1 and breast cancer: SERENA 1 is a phase I, open-label, dose-dependent exposure trial that analyzed the safety, tolerability, and preliminary clinical efficacy of camizestrant monotherapy (part A (escalation)/part B (expansion)) and in combination with palbociclib (parts C/D), everolimus (E/F), abemaciclib (G/H), and capivasertib (I/J) in pretreated women with ER+ HER2− advanced breast cancer.