Study of Pembrolizumab (MK-3475) Monotherapy Versus Sacituzumab Govitecan in Combination With Pembrolizumab for Participants With Metastatic Non-small Cell Lung Cancer (NSCLC) With Programmed Cell Death Ligand 1 (PD-L1) Tumor Proportion Score (TPS) ≥50% (MK-3475-D46)

Prior treatment

• Has received prior systemic chemotherapy or other targeted or biological antineoplastic therapy for their metastatic NSCLC
• Has previously received treatment with Topoisomerase 1 inhibitors or Trop-2 targeted therapy
• Has received prior therapy with an anti-programmed cell death 1 protein (anti-PD-1), anti-programmed cell death ligand 1 (anti-PD-L1), or anti anti- programmed cell death ligand 2 (PD-L2) agent or with an agent directed to another stimulatory or coinhibitory T-cell receptor
• Has received prior radiotherapy within 2 weeks of start of study intervention or has radiation-related toxicities requiring corticosteroids
• Has received radiation therapy to the lung that is \>30 Gray (Gy) within 6 months of the first dose of study intervention
• Has received a live or live-attenuated vaccine within 30 days before the first dose of study intervention
• Has received an investigational agent or has used an investigational device within 4 weeks before study intervention administration
• Has diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy or any other form of immunosuppressive therapy within 7 days prior the first dose of study medication
• Have not adequately recovered from major surgery or have ongoing surgical complications

Other illness

• Has history of a second malignancy, unless potentially curative treatment has been completed with no evidence of malignancy for 3 years
• Has active chronic inflammatory bowel disease
• Has severe hypersensitivity (≥Grade 3) to pembrolizumab or sacituzumab govitecan and/or any of their excipients
• Has active autoimmune disease that has required systemic treatment in past 2 years except replacement therapy
• History of (noninfectious) pneumonitis/interstitial lung disease that required steroids or has current pneumonitis/interstitial lung disease
• Has active infection requiring systemic therapy
• Has history of human immunodeficiency virus (HIV) infection
• History of hepatitis B or known active hepatitis C virus infection

Lab values

• Has cardiac disease
  • Myocardial infarction or unstable angina pectoris within 6 months of enrollment
  • History of serious ventricular arrhythmia, high-grade atrioventricular block, or other cardiac arrhythmias requiring antiarrhythmic medications; history of QT interval prolongation
  • New York Heart Association (NYHA) Class III or greater congestive heart failure or left ventricular ejection fraction of \<40%
• Has history or current evidence of any condition, therapy, laboratory abnormality, or other circumstance that might confound the results of the study or interfere with the participant's participation for the full duration of the study, such that it is not in the best interest of the participant to participate, in the opinion of the treating investigator

Other

• The main exclusion criteria include but are not limited to the following:
• Has known active central nervous system (CNS) metastases and/or carcinomatous meningitis

• The main inclusion criteria include but are not limited to the following:
• Has a histologically or cytologically confirmed diagnosis of metastatic non-small cell lung cancer (NSCLC)
• Has confirmation that epidermal growth factor receptor (EGFR), anaplastic lymphoma kinase 1 (ALK-1), or ROS proto-oncogene 1 (ROS-1)-directed therapy is not indicated as primary therapy
• Has provided tumor tissue that demonstrates PD-L1 tumor proportion score (TPS) ≥50% of tumor cells as assessed by immunohistochemistry (IHC) at a central laboratory
• Has a life expectancy of at least 3 months