RecruitingPhase 2Combination productStudy of Palliative Radiation Combined with Pembrolizumab in Unresectable Metastatic Stage IV Breast CancerThis is a phase 2, open-label, single-arm trial designed to evaluate the efficacy and safety of stereotactic body radiation therapy (SBRT) in combination with pembrolizumab following disease progression after two prior lines of standard therapy in unresectable metastatic stage IV breast cancer