Safety and Efficacy Study of Pemetrexed + Platinum Chemotherapy + Pembrolizumab (MK-3475) With or Without Lenvatinib (MK-7902/E7080) as First-line Intervention in Adults With Metastatic Nonsquamous Non-small Cell Lung Cancer (MK-7902-006/E7080-G000-315/LEAP-006)-China Extension Study

Inclusion Criteria

• Histologically or cytologically confirmed diagnosis of Stage IV (American Joint Committee on Cancer [AJCC], version 8 or current version) nonsquamous NSCLC.
• Confirmation that Epidermal Growth Factor Receptor (EGFR), ALK Receptor Tyrosine Kinase (ALK), or ROS1 Receptor Tyrosine Kinase (ROS1)-directed therapy is not indicated as primary treatment (documentation of absence of tumor-activating EGFR mutations AND absence of ALK and ROS1 gene rearrangements OR presence of a Kirsten Rat Sarcoma (KRAS) gene mutation).
• Have measurable disease based on RECIST 1.1. Note: Lesions that appear measurable, but are situated in a previously irradiated area, can be considered measurable (eligible for selection as target lesions) if they have shown documented growth since the completion of radiation.
• Provided an evaluable archival tumor tissue sample or newly obtained core or excisional biopsy of a tumor lesion (that was not previously irradiated) for central PD-L1 testing.
• Life expectancy of at least 3 months.
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 within 7 days prior to the first dose of study intervention but before randomization.
• Male participants must agree to use contraception during the treatment period and for at least 120 days after the last dose of pembrolizumab and/or lenvatinib/matching placebo and up to 180 days after the last dose of chemotherapeutic agents. A male participant must also agree to the following: 1) abstinence from heterosexual intercourse as their preferred and usual lifestyle (abstinent on a long term and persistent basis) and agree to remain abstinent, OR 2) agree to use a male condom plus partner use of an additional contraceptive method when having penile-vaginal intercourse with a woman of childbearing potential (WOCBP) who is not currently pregnant, unless confirmed to be azoospermic (vasectomized or secondary to medical cause). Note: Men with a pregnant or breastfeeding partner must agree to remain abstinent from penile-vaginal intercourse or use a male condom during each episode of penile-vaginal penetration.
• Female participant is eligible to participate if she is not pregnant or breastfeeding, and at least one of the following conditions applies: 1) not a WOCBP OR 2) a WOCBP and using a contraceptive method that is highly effective (with a failure rate of 150/90 mm Hg for >4 weeks despite standard medical management.

Exclusion Criteria

• Known untreated central nervous system (CNS) metastases and/or carcinomatous meningitis. Participants with previously treated brain metastases may participate provided they are radiologically stable, clinically stable, and have not required steroids for at least 14 days prior to the first dose of study intervention.
• History of (noninfectious) pneumonitis that required systemic steroids or current pneumonitis/interstitial lung disease.
• Radiographic evidence of major blood vessel invasion/infiltration.
• Known history of an additional malignancy, except if the participant has undergone potentially curative therapy with no evidence of that disease recurrence for at least 3 years since initiation of that therapy. Note: The time requirement also 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.
• Active autoimmune disease that has required systemic treatment in the past 2 years (i.e., with use of disease-modifying agents, corticosteroids, or immunosuppressive drugs). Replacement therapy (e.g., thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency, etc.) is allowed.
• Diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy (doses exceeding 10 mg daily of prednisone equivalent) or any other form of immunosuppressive therapy within 7 days prior the first