This study looks at how well two drugs, belzutifan and fulvestrant, work together compared to another treatment option for a type of breast cancer called ER+/HER2- metastatic breast cancer. Metastatic means the cancer has spread to other parts of the body. ER+ means the cancer grows in response to the hormone estrogen, while HER2- means the cancer does not have a protein called human epidermal growth factor receptor 2. Belzutifan and fulvestrant are being tested against everolimus with other hormone therapies. Everolimus is a drug that helps stop cancer cells from growing. **Key Points:** - **Study Duration:** Participants will need to visit the study site regularly. The exact length of the study isn't specified, but check with the study team. - **Participation Requirements:** You must have ER+/HER2- breast cancer that cannot be treated with surgery and must meet specific health criteria. You should not have certain medical conditions or past treatments that might interfere with the study drugs. - **Risks and Benefits:** Consider potential side effects of the drugs involved and whether participating could potentially help manage your cancer. Always discuss with your doctor before joining.