Belzutifan Plus Fulvestrant for ER+/​HER2- Metastatic Breast Cancer

To find out if belzutifan plus fulvestrant works better than everolimus plus endocrine therapy in helping people with ER-positive, HER2-negative metastatic breast cancer live longer, feel better, and delay cancer progression.

• Adults 18+ years of age
• Diagnosed with estrogen receptor-positive (ER+), HER2-negative breast cancer that cannot be removed by surgery (unresectable) and has spread beyond the breast (metastatic)

• Intravenous (IV) or oral medication depending on the treatment group
• Treatment with either belzutifan plus fulvestrant, or everolimus plus endocrine therapy (fulvestrant or exemestane)
• CT/MRI scans to check response to treatment
• Blood and urine tests to monitor your health and treatment effects
• Electrocardiogram (ECG) to monitor heart function
• Questionnaires