Testing the PD-1 Inhibitor Pembrolizumab as Maintenance Therapy After Initial Chemotherapy in Metastatic Bladder Cancer

OUTLINE: This is a multi-center trial. Eligible subjects will be 1:1 randomized to placebo (Control Arm A) and pembrolizumab (Experimental Arm B). Stratification factors for randomization: presence of visceral metastatic disease (lung, liver, or bone or other organs vs. lymph node only) at the time of initiation of first-line chemotherapy, and response to first-line chemotherapy (CR/PR vs. SD. Subjects who progress on placebo will be assessed to determine if they are eligible to cross over to unblinded treatment with pembrolizumab. INVESTIGATIONAL TREATMENT: For Control Arm A, commercially available normal saline will be used as the placebo. No active placebo drug will be mixed with the normal saline. For Experimental Arm B, pembrolizumab (or placebo), 200 mg intravenous infusion (IV) every 3 weeks for up to 12 months, or until progressive disease (PD) or unacceptable toxicity. The following required laboratory values must be obtained within fourteen days prior to registration for protocol therapy: Hematopoietic: * Absolute neutrophil count (ANC) ≥1,500 /mcL * Platelets ≥100,000 / mcL * Hemoglobin ≥8.5 g/dL Renal: * Creatinine ≤1.5x ULN OR * Measured or calculated creatinine clearance ≥30 mL/min for subject with creatinine levels \>1.5x institutional ULN * GFR can also be used in place of creatinine or CrCl Hepatic: * Serum total bilirubin ≤ 1.5 X ULN OR * Direct bilirubin ≤ ULN for subjects with total bilirubin levels \> 1.5 ULN * AST (SGOT) and ALT (SGPT) ≤ 2.5 X ULN OR ≤ 5 X ULN for subject with liver metastases Coagulation: * International Normalized Ratio (INR) or Prothrombin Time (PT) ≤1.5 X ULN. If subject is on anticoagulant therapy, PT or PTT must be within therapeutic range of intended use of anticoagulants.