Radiation Therapy and M7824 in Treating Patients With Metastatic Hormone Receptor Positive, HER2 Negative Breast Cancer

This phase I trial studies the side effects and best dose of anti-PD-L1/TGFbetaRII fusion protein M7824 (M7824) when given together with radiation therapy in treating patients with hormone receptor positive, HER2 negative breast cancer that has spread to other parts of the body. Radiation therapy uses high energy x-rays to kill tumor cells and shrink tumors. M7824 is a drug that targets specific proteins on immune cells in order to activate immune responses against tumor cells. Giving M7824 together with radiation therapy may work better in treating patients with breast cancer.