A Randomized Trial of Maintenance Systemic Therapy After Radiation for Oligometastatic Renal Cell Carcinoma (ASTROs)

Primary Objectives: * To evaluate PFS in patients randomized to definitive RT followed by pembrolizumab versus definitive RT followed by observation. Secondary Objectives: Secondary Objective #1: * To evaluate overall survival (OS) in patients randomized to definitive RT followed by maintenance pembrolizumab versus definitive RT followed by observation. Secondary Objective #2: * To evaluate time to next line systemic therapy (defined as systemic therapy given after pembrolizumab) in patients randomized to definitive RT followed by maintenance pembrolizumab versus definitive RT followed by observation. Secondary Objective #3: * To evaluate local recurrence free survival (LRFS) in patients randomized to definitive RT followed by maintenance pembrolizumab versus definitive RT followed by observation. Secondary Objective #4: * To evaluate distant recurrence free survival (DRFS) in patients randomized to definitive RT followed by maintenance pembrolizumab versus definitive RT followed by observation. Secondary Objective #5: * To evaluate estimate PFS2, LRFS2, and DRFS2 in patients who crossed over from one randomization arm to the other arm. Secondary Objective #6: * To evaluate frequency of adverse events (AEs) in patients randomized to definitive RT followed by maintenance pembrolizumab versus definitive RT followed by observation. Exploratory Objectives: Exploratory Objective #1: * To determine the association of translational biomarkers including peripheral blood markers and tissue markers with patient outcomes. Exploratory Objective #2: * To determine changes in translational biomarkers including peripheral blood markers and tissue markers after receipt of definitive RT. Exploratory Objective #3: -To estimate PFS2, LRFS2, and DRFS2 in patients who crossed over from one randomization arm to the other arm.