This study is about comparing two treatments, **giredestrant** and **fulvestrant**, for a type of breast cancer called ER-positive, HER2-negative advanced breast cancer. ER-positive means the cancer grows in response to estrogen, and HER2-negative means it lacks a protein that can promote cancer growth. Participants should have cancer that has stopped responding to previous hormone treatments. The study will test these drugs with other medicines called **CDK4/6 inhibitors** (like palbociclib, ribociclib, or abemaciclib). CDK4/6 inhibitors help stop cancer cells from growing. This is a Phase III study, meaning the drugs have already been tested for safety and effectiveness in earlier studies.

• The study is "open-label", so both doctors and patients know which treatment is given.
• Participants must not have received certain other cancer treatments before.
• Participants will need to commit to ongoing treatment, possibly including injections, for the study's duration.

Consider joining if you meet the criteria and are open to the treatment plan. This study aims to find safer and more effective treatments for advanced breast cancer.