Summary
The main purpose of this study is to measure how well imlunestrant works compared to
standard hormone therapy in participants with early breast cancer that is estrogen
receptor positive (ER+) and human epidermal receptor 2 negative (HER2-). Participants
must have already taken endocrine therapy for two to five years and must have a
higher-than-average risk for their cancer to return. Study participation could last up to
10 years.