Inclusion Criteria:

          -  Documentation of disease

               -  Histologic documentation: Histologically or cytologically confirmed urothelial
                  carcinoma (UC) with predominantly transitional-cell features

               -  Stage: Locally advanced or metastatic disease prior to starting immune checkpoint
                  blockade

               -  Tumor Site: Bladder, renal pelvis, ureter, or urethra

          -  Patients must be receiving current active treatment with standard of care (SOC) Food
             and Drug Administration (FDA) approved PD-1/L1 immune checkpoint inhibitor
             (ICI)-containing therapy for locally advance or metastatic UC

          -  Radiographic response 12-15 months after starting ICI-containing treatment, defined as
             any percent decrease in target and/or non-target lesion(s) criteria that is confirmed
             by repeat assessment(s) no less than 4 weeks after the criteria for response are first
             met without evidence of progressive disease

          -  Adequate bone marrow and organ functions to continue PD-1/L1 ICI as judged by the
             treating physician

          -  Eastern Cooperative Oncology Group (ECOG) performance status 0-2

          -  Central nervous system (CNS) metastasis is allowed if radiographically stable,
             clinically asymptomatic, and prior local therapy (if received) was completed > 6
             months before registration

        Exclusion Criteria:

          -  No toxicity from ICI therapy that makes continuation of treatment clinically
             unacceptable

          -  No history of tuberculosis, active hepatitis B (HBV) or hepatitis C (HCV), or
             uncontrolled human immunodeficiency virus (HIV)

               -  Patients with resolved HBV infection, defined as positive hepatitis B core
                  antibody (anti-Hb) and negative hepatitis B surface antigen (HbsAg), are eligible

               -  Patients with positive HCV antibody are eligible if HCV ribonucleic acid (RNA)
                  polymerase chain reaction (PCR) is negative

               -  Patients with HIV who are compliant with highly active antiretroviral therapy
                  (HAART) and have normal CD4 count and undetectable viral load are eligible

          -  No history of allogeneic organ transplantation

          -  No current immunosuppressive medication exceeding 10 mg/day of prednisone or its
             equivalent

             * Patients with pre-existing or treatment-emergent autoimmune or inflammatory
             disorders which do not require systemic immunosuppressive treatment exceeding 10
             mg/day of prednisone or its equivalent may be included

          -  No history of another primary malignancy except for malignancy treated with curative
             intent with no known active disease for >= 2 years, and adequately treated
             non-melanomatous skin cancer or carcinoma in situ (e.g. cervical carcinoma in situ
             [CIS]) without evidence of disease

          -  No female patients who are pregnant or breastfeeding, or male or female patients of
             reproductive potential who are not willing to employ effective birth control, because
             this study involves investigational agents whose genotoxic, mutagenic, and teratogenic
             effects on the developing fetus and newborn are unknown. Therefore, for women of
             childbearing potential only, a negative urine or serum pregnancy test pregnancy test
             done =< 14 days prior to registration is required