Study of Pembrolizumab (MK-3475) Subcutaneous (SC) Versus Pembrolizumab Intravenous (IV) Administered With Platinum Doublet Chemotherapy in Participants With Metastatic Squamous or Nonsquamous Non-Small Cell Lung Cancer (NSCLC) (MK-3475-A86)

Inclusion Criteria:

• Has pathologically (histologically or cytologically) confirmed diagnosis of squamousor nonsquamous non-small cell lung cancer (NSCLC)

• Has Stage IV (T any, N any, M1a, M1b, or M1c - American Joint Committee on Cancer 8th Edition) squamous or nonsquamous NSCLC

• Has confirmation that epidermal growth factor receptor (EGFR), Anaplastic lymphomakinase (ALK), or ROS Proto-Oncogene 1, Receptor Tyrosine Kinase (ROS1)-directedtherapy is not indicated in nonsquamous NSCLC as well as mixed nonsquamous/squamousNSCLC. Participants with purely squamous NSCLC do not require testing

• Has not received prior systemic treatment for their metastatic NSCLC. Participantswho received adjuvant or neoadjuvant therapy are eligible if theadjuvant/neoadjuvant therapy was completed at least 12 months prior to thedevelopment of metastatic disease

• Has an Eastern Cooperative Oncology Group (ECOG) performance score (PS) of 0 or 1

• Male participants are eligible to participate if they agree to use contraception asper protocol unless confirmed to be azoospermic

• A female participant is eligible to participate if she is not pregnant orbreastfeeding, and at least one of the following conditions applies: is not a womanof childbearing potential (WOCBP) or is a WOCBP who agrees of using a contraceptivemethod per protocol

• Has measurable disease per Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST 1.1) as assessed by the local site investigator/radiology

• Submit an archival tumor tissue sample or newly obtained core or incisional biopsyof a tumor lesion not previously irradiated for PD-L1 status determination prior torandomization

• Has adequate organ function

Exclusion Criteria:

• Has a known additional malignancy that is progressing or has required activetreatment within the past 3 years

• Has known central nervous system (ie, brain and/or spinal cord) metastases and/orcarcinomatous meningitis. Participants with treated brain metastases may participateonly if they satisfy all of the following: a) Have no evidence of new or enlargingbrain metastases confirmed by post-treatment repeat brain imaging performed at least 4 weeks after pretreatment brain imaging, and b) Are neurologically stable withoutthe need for steroids for at least 14 days before first dose of trial treatment asper local site assessment

• Has severe hypersensitivity to study intervention and/or any of its excipients

• Has an active autoimmune disease that has required systemic treatment in past 2years

• Has a history of (noninfectious) pneumonitis/interstitial lung disease that requiredsteroids or has current pneumonitis/interstitial lung disease

• Has an active infection requiring systemic therapy

• Has a known history of human immunodeficiency virus (HIV) infection and/or HepatitisB infection or known active Hepatitis C infection

• Has a known psychiatric or substance abuse disorder that would interfere with theparticipant's ability to cooperate with the requirements of the study

• Has symptomatic ascites or pleural effusion. A participant who is clinically stableafter treatment for these conditions is eligible

• Before the first dose of study intervention: a) Has received prior systemiccytotoxic chemotherapy for metastatic NSCLC b) Has received antineoplasticbiological therapy for metastatic NSCLC c) Has had major surgery (<3 weeks prior tofirst dose) d) Has received prior therapy with an anti-programmed cell death 1 (anti-PD-1), anti-programmed cell death ligand 1 (anti-PD-L1), or anti-programmedcell death ligand 2 (anti-PD-L2) agent or with an agent directed to anotherstimulatory or coinhibitory T-cell receptor

• Received radiation therapy to the lung that is >30 Gray within 6 months of the firstdose of study intervention

• Is expected to require any other form of antineoplastic therapy while on study

• For participants with nonsquamous histology: Is unable to interrupt aspirin or otherNon-steroidal anti-inflammatory drugs (NSAIDs), other than an aspirin dose ≤1.3g/day, for a 5-day period

• For participants with nonsquamous histology: Is unable or unwilling to take folicacid or vitamin B12 supplementation

• Has received prior radiotherapy within 2 weeks of start of study intervention orhave had a history of radiation pneumonitis. Participants must have recovered fromall radiation-related toxicities and not require corticosteroids. A 1-week washoutis permitted for palliative radiation (≤2 weeks of radiotherapy) to non-CNS disease

• Has received a live or live attenuated vaccine within 30 days prior to the firstdose of study intervention

• Is currently participating in or has participated in a study of an investigationalagent or has used an investigational device within 4 weeks prior to the first doseof study intervention

• Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapyor any other form of immunosuppressive therapy within 7 days prior the first dose ofstudy intervention

• Has had an allogenic tissue/solid organ transplant