Pembrolizumab + Epacadostat vs Pembrolizumab + Placebo in Recurrent or Progressive Metastatic Urothelial Carcinoma

Inclusion Criteria:

* Histologically-confirmed diagnosis of urothelial carcinoma of the renal pelvis, ureter, bladder, or urethra, that is transitional cell, or mixed transitional/non-transitional (predominantly transitional) cell type.
* Progression or recurrence of urothelial carcinoma following one prior platinum containing chemotherapy regimen for metastatic or unresectable locally advanced disease. A participant who receives a neoadjuvant or adjuvant platinum-containing regimen following cystectomy for localized muscle-invasive urothelial carcinoma is acceptable (without further systemic treatment), if recurrence/progression occurs ≤ 12 months following completion of therapy.
* Measurable disease based on RECIST v1.1.
* Have provided an archival tumor tissue sample or newly obtained core or excisional biopsy of a tumor lesion not previously irradiated for PD-L1 analysis.
* Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
* Adequate organ function per protocol-defined criteria.

Exclusion Criteria:

* Urothelial carcinoma that is suitable for local therapy with curative intent.
* History or presence of an abnormal electrocardiogram (ECG) that, in the investigator's opinion, is clinically meaningful.
* Known additional malignancy that is progressing or has required active treatment within the past 3 years.
* Known active central nervous system (CNS) metastases and/or carcinomatous meningitis. Participants with previously treated brain metastases may participate provided they are radiologically stable, ie, without evidence of progression for at least 4 weeks by repeat imaging.
* Active autoimmune disease that has required systemic treatment in past 2 years.
* Known history of human immunodeficiency virus (HIV) infection. HIV testing is not required unless mandated by local health authority.
* Known history of or is positive for active hepatitis B (HBsAg reactive) or has active hepatitis C (HCV RNA). Note: Testing must be performed to determine eligibility.
* Use of protocol-defined prior/concomitant therapy.