Safety and Efficacy of MK-1200 in Participants With Advanced Solid Tumors (MK-1200-002)

Inclusion Criteria:

• Confirmed advanced (unresectable and/or metastatic) solid tumor: gastric cancer (including gastroesophageal junction cancer), esophageal cancer, biliary tractcancer, or pancreatic ductal adenocarcinoma

• Participants who experienced Adverse Events (AEs) due to previous anticancertherapies must have recovered to < Grade 1 or baseline

• Human immunodeficiency virus (HIV)-infected participants must have well controlledHIV on antiretroviral therapy

• Hepatitis B surface antigen (HBsAg) positive participants are eligible if they havereceived Hepatitis B Virus (HBV) antiviral therapy for at least 4 weeks and haveundetectable HBV viral load

• Participants with a history of Hepatitis C Virus (HCV) infection are eligible if HCVviral load is undetectable

• Received and progressed on or after 1 or 2 prior lines of therapy

Exclusion Criteria:

• Active severe digestive disease

• History of acute myocardial infarction; unstable angina; stroke or transientischemic attack within 6 months prior to the first dose of study intervention

• Diabetes or hypertension that cannot be controlled by medication

• HIV-infected participants with a history of Kaposi's sarcoma and/or MulticentricCastleman's Disease

• Received prior systemic anticancer therapy including investigational agents within 4weeks before study intervention

• Received prior radiotherapy within 2 weeks of start of study intervention, or hasradiation-related toxicities, requiring corticosteroids

• Known additional malignancy that is progressing or has required active treatmentwithin the past 2 years

• Known active central nervous system (CNS) metastases and/or carcinomatous meningitis

• Active infection requiring systemic therapy

• Have not adequately recovered from major surgery or have ongoing surgicalcomplications