Combined Immunotherapies in Metastatic ER+ Breast Cancer

This study tests adding immunotherapy (checkpoint inhibitors) to standard hormone-blocking treatment with CDK4/6 inhibitors (drugs that slow cancer cell division) in patients with hormone receptor-positive, HER2-negative metastatic breast cancer. **You may be eligible if...** - You are 18 or older with hormone receptor-positive (HR+), HER2-negative metastatic breast cancer - You have 5 or fewer measurable sites of disease - You are eligible for treatment with a CDK4/6 inhibitor plus an aromatase inhibitor - You are pre- or post-menopausal (male patients are also eligible) - Your cancer has progressed on at least one prior hormone therapy **You may NOT be eligible if...** - You have more than 5 sites of measurable disease - You have had more than one prior line of systemic therapy for metastatic disease - You have uncontrolled brain metastases - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.