This study is for people with **early breast cancer** that is *estrogen receptor (ER)-positive* and *HER2-negative*. These terms mean that the cancer grows in response to estrogen (a hormone) and does not have a protein called HER2 that can make cancer grow faster. The study compares a new drug called **giredestrant** to another type of regular treatment called **endocrine therapy**. Endocrine therapy is a treatment that stops cancer cells from using the hormone estrogen to grow. Participants in this study must have undergone surgery and may have received other treatments like chemotherapy or radiation before joining.

An additional part of the study will test giredestrant with another medicine, **abemaciclib**, in some participants to see if the combination is safe and effective.

• Participants must be able to swallow pills and should not have serious liver or heart problems.
• Pregnant or breastfeeding individuals cannot join the study.
• The study involves taking medication and regular health check-ups.