A Study of Pembrolizumab Plus Epacadostat With Platinum-based Chemotherapy Versus Pembrolizumab Plus Platinum-based Chemotherapy Plus Placebo in Metastatic Non-Small Cell Lung Cancer (KEYNOTE-715-06/ECHO-306-06)

Inclusion Criteria: * Histologically or cytologically confirmed diagnosis of stage IV NSCLC without epidermal growth factor receptor (EGFR)-sensitizing mutation, ROS1 and/or anaplastic lymphoma kinase (ALK) translocation * Measurable disease based on RECIST 1.1 * Life expectancy of at least 3 months. * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. * Adequate organ function per protocol-defined criteria. * Provide tumor tissue sample. Exclusion Criteria: * Known untreated central nervous system metastases and/or carcinomatous meningitis * History of (non-infectious) pneumonitis that required systemic steroids or current pneumonitis/interstitial lung disease. * Symptomatic ascites or pleural effusion. * Known history of an additional malignancy, except if the participant has undergone potentially curative therapy with no evidence of that disease recurrence for 5 years since initiation of that therapy. * Active autoimmune disease that has required systemic treatment in past 2 years. * Has had an allogeneic tissue/solid organ transplant. * Has a known history of human immunodeficiency virus (HIV) infection. HIV testing is not required unless mandated by the local health authority. * Has 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. * History or presence of an abnormal electrocardiogram (ECG) that, in the Investigator's opinion, is clinically meaningful. * Use of protocol-defined prior/concomitant therapy.