Efficacy and Safety Study of Pembrolizumab (MK-3475) With or Without Lenvatinib (MK-7902/E7080) in Adults With Programmed Cell Death-Ligand 1 (PD-L1)-Positive Treatment-naïve Nonsmall Cell Lung Cancer (NSCLC) (MK-7902-007/E7080-G000-314/LEAP-007)

Inclusion Criteria:

Has a histologically or cytologically confirmed diagnosis of NSCLC.
Has Stage IV NSCLC (American Joint Committee on Cancer [AJCC 8th edition]).
Has measurable disease based on RECIST 1.1.
Has tumor tissue that demonstrates programmed cell death-ligand 1 (PD-L1) expression in ≥1% of tumor cells (Tumor Proportion Score [TPS] ≥1%) as assessed by immunohistochemistry (IHC) 22C3 pharmDx assay (Dako North America, Inc.) at a central laboratory.
Has a life expectancy of ≥3 months.
Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 within 7 days before the first dose of study treatment but before randomization.
Male participants must agree to the following during the treatment period and for ≥7 days after the last dose of lenvatinib/matching placebo: 1) Be abstinent from heterosexual intercourse as their preferred and usual lifestyle and agree to remain abstinent, OR 2) Must agree to use contraception unless confirmed to be azoospermic (vasectomized or secondary to medical cause).
Female participants are eligible to participate if not pregnant or breastfeeding, and ≥1 of the following applies: 1) Is not a woman of child-bearing potential (WOCBP), OR 2) Is a WOCBP and is using a highly effective contraceptive method that has a low user dependency, or be abstinent from heterosexual intercourse as their preferred and usual lifestyle during the treatment period and for ≥120 days post pembrolizumab or ≥30 days post lenvatinib/matching placebo, whichever occurs last.
Has adequately controlled blood pressure (BP) with or without antihypertensive medications, defined as BP ≤150/90 mm Hg and no change in antihypertensive medications within 1 week before randomization.
Has adequate organ function.

Exclusion Criteria:

Has known untreated central nervous system metastases and/or carcinomatous meningitis.
Has active hemoptysis (at least 0.5 teaspoon of bright red blood) within 2 weeks prior to the first dose of study intervention.
Has radiographic evidence of intratumoral cavitations, encasement, or invasion of a major blood vessel.
Has a known history of an additional malignancy, except if the participant has undergone potentially curative therapy with no evidence of that disease recurrence for ≥3 years since initiation of that therapy. (Note: The time requirement does not apply to participants who underwent successful definitive resection of basal cell carcinoma of the skin, superficial bladder cancer, squamous cell carcinoma of the skin, in situ cervical cancer, or other in situ cancers.)
Has an active autoimmune disease that has required systemic treatment in the past 2 years. Replacement therapy (e.g. thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency, etc.) is not considered a form of systemic treatment and is allowed.
Has had an allogeneic tissue/solid organ transplant.
Has a known history of human immunodeficiency virus (HIV) infection.
Has a history of (noninfectious) pneumonitis that required systemic steroids or current pneumonitis/interstitial lung disease.
Has a known history of hepatitis B or known active hepatitis C virus infection.
Has a history of a gastrointestinal condition or procedure that in the opinion of the investigator may affect oral study drug absorption.
Has significant cardiovascular impairment within 12 months of the first dose of study treatment, such as a history of congestive heart failure greater than New York Heart Association Class II, unstable angina, myocardial infarction, cerebrovascular accident/stroke, or cardiac arrhythmia associated with hemodynamic instability.
Has not recovered adequately from any toxicity and/or complications from major surgery before starting study treatment.
Has a known history of active tuberculosis (TB).
Has an active infection requiring systemic therapy.
Has previously had a severe hypersensitivity reaction to treatment with a monoclonal antibody or has a known sensitivity or intolerance to any component of lenvatinib or pembrolizumab.
Has received prior systemic chemotherapy or other targeted or biological antineoplastic therapy for their metastatic NSCLC.
Has received prior therapy with an anti-PD-1, anti-PD-L1, or anti-PD-L2 agent or with an agent directed to another stimulatory or co-inhibitory T-cell receptor (e.g. cytotoxic T-lymphocyte-associated protein 4 [CTLA-4], Tumor necrosis factor receptor superfamily, member 4 [OX 40], tumor necrosis factor receptor superfamily member 9 [CD137]) or has received lenvatinib as monotherapy or in combination with anti- programmed cell death protein (anti-PD-1) agents.
Has received radiotherapy within 14 days before the first dose of study treatment or received lung radiation therapy of >30 Gray (Gy) within 6 months before the first dose of study treatment. (Note: Participants must have recovered from all radiation-related toxicities to ≤Grade 1, not require corticosteroids, and not have had radiation pneumonitis.)
Has a diagnosis of immunodeficiency or is receiving any form of immunosuppressive therapy within 7 days before the first dose of study treatment.
Is receiving systemic steroid therapy (doses >10 mg daily of prednisone equivalent) within 7 days before the first dose of study treatment.
Has received a live or attenuated vaccine within 30 days before the first dose of study treatment.
Has had major surgery within 3 weeks prior to first dose of study treatment
Has pre-existing ≥Grade 3 gastrointestinal or nongastrointestinal fistula.