Pembrolizumab (MK3475), Gemcitabine, and Concurrent Hypofractionated Radiation Therapy for Muscle-Invasive Urothelial Cancer of the Bladder

Inclusion Criteria: * Histologically confirmed muscle-invasive urothelial cancer of the bladder within 60 days of study enrollment. Patients must be willing to provide a TURBT specimen during screening and prior to enrollment if adequate specimen (FFPE tissue block or 20 unstained slides) from initial TURBT documenting muscle-invasive urothelial bladder cancer is not available. * Clinical stage T2-T4a, N0, M0 urothelial bladder cancer. * Deemed to not be a candidate for radical cystectomy by attending urologic oncologist or refuse radical cystectomy. * Be willing and able to provide written informed consent/assent for the trial. * Be ≥ 18 years of age on day of signing informed consent. * Have a performance status of 0 or 1 on the Eastern Cooperative Oncology Group Performance Scale. * Demonstrate adequate organ function as defined below, all screening labs should be performed within 10 days of protocol enrollment. * Absolute neutrophil count \>= 1,500 /mcL; * Platelets \>= 100,000 /mcL; * Hemoglobin \>= 9.0 g/dL; * Serum creatinine \<=1.5 x upper limit of normal (ULN) or calculated creatinine clearance \>= 30 mL/min as calculated by Cockcrof-Gault formaulae or by 24 hour urine collection; * Serum total bilirubin \<=1.5 x ULN or direct bilirubin \<= ULN for subjects with total bilirubin levels \> 1.5 x ULN; * Aspartate aminotransferase and alanine aminotransferase \<= 1.5 x ULN; * Albumin \>= 2.5 mg/dL; * International normalized ratio or prothrombin time (P…