A Phase 3 Study of Pembrolizumab + Epacadostat or Placebo in Subjects With Unresectable or Metastatic Melanoma (Keynote-252 / ECHO-301)

Inclusion Criteria: * Have histologically or cytologically confirmed melanoma * Have unresectable Stage III or Stage IV melanoma, as per AJCC staging system not amenable to local therapy * A minimum of 1 measurable lesion by CT or MRI * Provide a baseline tumor biopsy * Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1 Exclusion Criteria: * Has received prior systemic treatment for unresectable or metastatic melanoma (except BRAF directed therapy) * Has received prior therapy with an anti-PD-1, anti-PD-L1, anti-PD-L2, anti-CD137, or IDO1 inhibitor or any other antibody or drug specifically targeting checkpoint pathways other than anti-CTLA-4 which is permitted in the adjuvant setting * Has received prior adjuvant therapy, monoclonal antibody or an investigational agent or device within 4 weeks or 5 half-lives (whichever is longer) * Has an active infection requiring systemic therapy * Has known history of human immunodeficiency virus (HIV) (HIV 1/2 antibodies) * Has known history of or is positive for Hepatitis B or Hepatitis C * Is pregnant or breastfeeding or expecting to conceive or father children within the projected duration of the study, starting with the screening visit through 120 days after the last dose of study treatment