Study of Pembrolizumab (MK-3475) Versus Platinum-Based Chemotherapy for Participants With Programmed Cell Death-Ligand 1 (PD-L1)-Positive Advanced or Metastatic Non-Small Cell Lung Cancer (MK-3475-042/KEYNOTE-042)

Inclusion criteria:

* Histologically- or cytologically-confirmed diagnosis of advanced or metastatic NSCLC
* PD-L1 positive tumor
* Measureable disease based on Response Evaluation Criteria in Solid Tumors (RECIST) 1.1
* Life expectancy of at least 3 months
* No prior systemic chemotherapy for the treatment of the participant's advanced or metastatic disease (treatment with chemotherapy and/or radiation as part of neoadjuvant/adjuvant therapy is allowed as long as completed at least 6 months prior to diagnosis of advanced or metastatic disease)
* Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1
* Adequate organ function
* No prior malignancy, with the exception of basal cell carcinoma of the skin, superficial bladder cancer, squamous cell carcinoma of the skin, or in situ cancer, or has undergone potentially curative therapy with no evidence of that disease recurrence for 5 years since initiation of that therapy
* Submission of formalin-fixed diagnostic tumor tissue (in the case of participants having received adjuvant systemic therapy, the tissue should be taken after completion of this therapy)
* Female participants of childbearing potential must have a negative urine or serum pregnancy test and must be willing to use two adequate barrier methods of contraception or a barrier method plus a hormonal method starting with the screening visit through 120 days after the last dose of pembrolizumab or 180 days after the last dose of chemotherapeutic agents used in the study
* Male participants with a female partner(s) of child-bearing potential must be willing to use two adequate barrier methods of contraception from screening through 120 days after the last dose of pembrolizumab or 180 days after the last dose of chemotherapeutic agents used in the study

Exclusion criteria:

* Epidermal growth factor receptor (EGFR)-sensitizing mutation and/or is echinoderm microtubule-associated protein-like 4(EML4) gene/anaplastic lymphoma kinase (ALK) gene fusion positive
* Currently participating or has participated in a study of an investigational agent or using an investigational device within 4 weeks of the first dose of study therapy
* No tumor specimen evaluable for PD-L1 expression by the central study laboratory
* Squamous histology and received carboplatin in combination with paclitaxel in the adjuvant setting
* Is receiving systemic steroid therapy ≤3 days prior to the first dose of study therapy or receiving any other form of immunosuppressive medication with the exception of daily steroid replacement therapy
* The NSCLC can be treated with curative intent with either surgical resection and/or chemoradiation
* Expected to require any other form of systemic or localized antineoplastic therapy while on study
* Any prior systemic cytotoxic chemotherapy, biological therapy or major surgery within 3 weeks of the first dose of study therapy; received lung radiation therapy \>30 Gy within 6 months of the first dose of study therapy
* Prior therapy with an anti-PD-1, anti-PD-L1, anti-PD-L2, anti-CD137, or anti-cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) antibody (including ipilimumab or any other antibody or drug specifically targeting T-cell co-stimulation or checkpoint pathways)
* Known central nervous system metastases and/or carcinomatous meningitis
* Active autoimmune disease that has required systemic treatment in the past 2 years
* Had allogeneic tissue/solid organ transplantation
* Interstitial lung disease or history of pneumonitis that has required oral or IV steroids
* Has received or will receive a live vaccine within 30 days prior to the first study therapy (seasonal flu vaccines that do not contain live vaccine are permitted)
* Active infection requiring intravenous systemic therapy
* Known history of human immunodeficiency virus (HIV)
* Known active Hepatitis B or C
* Regular user (including "recreational use") of any illicit drugs or had a recent history (within the last year) of substance abuse (including alcohol)
* Pregnant, breastfeeding, or expecting to conceive or father children within the projected duration of the study