A Study of MK-6837 as a Monotherapy and Combination Therapy in Participants With Advanced/Metastatic Solid Tumors (MK-6837-001)

The purpose of this study is to evaluate the safety, tolerability, and preliminary efficacy of MK-6837, administered as a monotherapy and in combination with pembrolizumab (MK-3475), in participants with histologically or cytologically confirmed advanced/metastatic solid tumors that have not responded to conventional therapy. There will not be any hypothesis testing in the study. As of Amendment 04 (effective date: 18-Dec-2025), there are no pharmacokinetic (PK) secondary outcome measures in this study.

Inclusion Criteria: The main inclusion criteria include but are not limited to the following: * Histologically or cytologically confirmed solid tumor by pathology report that is advanced or metastatic * Human Immunodeficiency Virus (HIV)-infected participants must have well controlled HIV on Antiretroviral Therapy (ART) * Participants who are Hepatitis B Surface Antigen (HBsAg) positive are eligible if they have received Hepatitis B Virus (HBV) antiviral therapy for at least 4 weeks, and have undetectable HBV viral load before allocation * Participants with history of Hepatitis C Virus (HCV) infection are eligible if HCV viral load is undetectable at screening Exclusion Criteria: The main exclusion criteria include but are not limited to the following: * Has not recovered to Common Terminology Criteria for Adverse Events (CTCAE) Grade 1 or better from any Adverse Events (AEs) that were due to cancer therapeutics administered more than 4 weeks earlier * History of a second malignancy, unless potentially curative treatment has been completed with no evidence of malignancy for 2 years * Has clinically significant cardiovascular disease * HIV-infected participants with a history of Kaposi's sarcoma and/or Multicentric Castleman's Disease * Received prior systemic anticancer therapy including investigational agents within 4 weeks before the first dose of study intervention * Has received any prior immunotherapy and was discontinued from that treatment due to a Grade 3 or higher immune-related AE (except endocrine disorders that can be treated with replacement therapy) or was discontinued from that treatment due to Grade 2 myocarditis or recurrent Grade 2 pneumonitis * Received prior radiotherapy within 2 weeks of start of study intervention, or has radiation-related toxicities, requiring corticosteroids * Received a live or live-attenuated vaccine within 30 days before the first dose of study intervention. Administration of killed vaccines is allowed * Diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy or any other form of immunosuppressive therapy within 7 days before the first dose of study intervention * Known additional malignancy that is progressing or has required active treatment within the past 2 years * Known active Central Nervous System (CNS) metastases and/or carcinomatous meningitis * Active autoimmune disease that has required systemic treatment in the past 2 years except replacement therapy * History of (noninfectious) pneumonitis/interstitial lung disease that required steroids or has current pneumonitis/interstitial lung disease * Active infection requiring systemic therapy * History of allogeneic tissue/solid organ transplant * Participants who have not adequately recovered from major surgery or have ongoing surgical complications