Study of Pembrolizumab (MK-3475) in Participants With Advanced Urothelial Cancer (MK-3475-052/KEYNOTE-052)

Inclusion Criteria:

* Histologically- or cytologically-confirmed diagnosis of advanced/unresectable (inoperable) or metastatic urothelial cancer of the renal pelvis, ureter, bladder, or urethra (transitional cell and mixed transitional/non-transitional cell histologies)
* Ineligible for cisplatin therapy
* No prior systemic chemotherapy for metastatic disease (adjuvant or neoadjuvant platinum-based chemotherapy with recurrence \>12 months since completion of therapy is allowed)
* Available tissue from a newly obtained core or excisional biopsy of a tumor lesion not previously irradiated
* Measurable disease
* Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1 or 2
* Adequate organ function
* Female participants of childbearing potential have a negative urine or serum pregnancy test; surgically sterile, or willing to use 2 acceptable methods of birth control, or abstain from heterosexual activity for the course of the study through 120 days after the last dose of study treatment
* Male participants must be willing to use an adequate method of contraception starting with the first dose of study medication through 120 days after the last dose of study treatment

Exclusion Criteria:

* Disease that is suitable for local therapy administered with curative intent
* Currently participating or has participated in a study of an investigational agent and received study therapy or used an investigational device within 4 weeks prior to the first dose of study treatment
* Prior anti-cancer monoclonal antibody (mAb) for direct anti-neoplastic treatment within 4 weeks prior to study Day 1 or who has not recovered from adverse events due to agents administered more than 4 weeks earlier
* Prior chemotherapy, targeted small molecule therapy, or radiation therapy within 2 weeks prior to study Day 1 or not recovered from AEs due to a previously administered agent
* Known additional malignancy that is progressing or requires active treatment excepting basal cell carcinoma of the skin, squamous cell carcinoma of the skin that has undergone potentially curative therapy, or in situ cancer
* Known active central nervous system (CNS) metastases and/or carcinomatous meningitis
* Active autoimmune disease that has required systemic treatment in past 2 years
* Evidence of interstitial lung disease or active non-infectious pneumonitis
* Active infection requiring systemic therapy
* Pregnant or breastfeeding, or expecting to conceive or father children within the projected duration of the trial, starting with the screening visit through 120 days after the last dose of study treatment
* Prior therapy with an anti-PD-1, anti-PD-L1, or anti-PD-L2 agent, or with an agent directed to another co-inhibitory T-cell receptor
* Known human immunodeficiency virus (HIV)
* Known active Hepatitis B or C
* Received a live virus vaccine within 30 days of planned start of study treatment