Anti-PD(L)1 and SBRT in the Treatment of Advanced, Platinum-Refractory Urothelial Carcinoma

Inclusion Criteria: * Subjects must have a histologic diagnosis of urothelial carcinoma * Subjects must have radiologic evidence of metastatic disease with measurable disease by RECIST 1.1 criteria other than the target lesion(s) for SBRT * Subjects must have at least 1 metastatic lesion previously not radiated that is amenable to SBRT per treating radiation oncologist. * Subjects must have had progression of disease within 12 months of platinum-containing chemotherapy (chemotherapy could have been given in the neoadjuvant, adjuvant or metastatic setting) for urothelial cancer * ECOG performance status of 0 to 2 (Eastern Cooperative Oncology Group Performance Status: an attempt to quantify cancer patients' general well-being and activities of daily life. The score ranges from 0 to 5 where 0 is asymptomatic and 5 is death.) * Absolute neutrophil count of ≥ 1000/mm3, platelet count ≥ 100,000/mm3, hemoglobin ≥ 8.0 g/dl; total bilirubin/ALT/AST \< 2.5 x upper limit of normal (patients with known gilbert disease who have serum bilirubin ≤3x ULN may be enrolled); serum creatinine \<3.0mg/dl or if elevated, a calculated estimated glomerular filtration rate (eGFR) of ≥30 mL/min/1.73 m2 * Subjects must have recovered to baseline or ≤ grade 1 CTCAE v 4.03 from toxicities related to any prior treatments unless AE(s) are clinically non-significant and/or stable on supportive therapy * Subjects must be ≥ 2 weeks from most recent systemic therapy or most recent radiation therapy * Women of childbearing potential must have a negative serum or urine pregnancy test within 28 days prior to registration. * Age ≥ 18 years Exclusion Criteria: * Prior treatment with anti-PD-1/PD-L1 and anti-CTLA-4 is NOT allowed. Prior intravesical BCG (Bacillus Calmette-Guerin) therapy is allowed * Treatment with any investigational agent or on an interventional clinical trial within 30 days prior to registration. * No prior or concurrent malignancy is allowed except for: adequately treated basal cell or squamous cell skin cancer, in situ cervical cancer, localized or locally advanced prostate cancer definitively treated without recurrence or with biochemical recurrence only, or any other cancer fully treated or from which the subject has been disease-free for at least 2 years. * Autoimmune diseases such as rheumatoid arthritis are NOT allowed. Vitiligo, mild psoriasis (topical therapy only) or hypothyroidism are allowed * Need for systemic corticosteroids \>10mg prednisone daily or equivalent alternative steroid * Any history of organ allografts * Any history of HIV or hepatitis B infection * Known brain metastases