This study is testing a new drug called imlunestrant to see if it works better than standard hormone treatment for people with early breast cancer. The cancer should be estrogen receptor positive (ER+) meaning the cancer grows with estrogen, and HER2-negative (HER2-), meaning it doesn't have too much of a protein called HER2. Participants should have already been on hormone therapy for 2 to 5 years and have a higher chance of the cancer coming back.

To be part of this study, participants need to have had a type of breast cancer that hasn’t spread far and have good organ function. They should not have had cancer spread to other body parts or had a long break in their past hormone treatment. They cannot be pregnant or breastfeeding. The study could last up to 10 years.

• The study could last up to 10 years.
• Participants must have taken hormone therapy for 2 to 5 years.
• Participants must have a higher risk of cancer returning.