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

The purpose of this study is to assess the efficacy and safety of MK-1200 monotherapy in participants with advanced/metastatic gastric/gastroesophageal junction (GEJ) cancer, esophageal cancer, biliary tract cancer, and pancreatic ductal adenocarcinoma who have received, or been intolerant to, all treatments known to confer clinical benefit. Part 1 of the study will be a dose escalation to determine the maximum tolerated dose (MTD). Part 2 will evaluate safety and efficacy of MK-1200 at 2 different doses

Inclusion Criteria: * Confirmed advanced (unresectable and/or metastatic) solid tumor: gastric cancer (including gastroesophageal junction cancer), esophageal cancer, biliary tract cancer, or pancreatic ductal adenocarcinoma * Participants who experienced Adverse Events (AEs) due to previous anticancer therapies must have recovered to \< Grade 1 or baseline * Human immunodeficiency virus (HIV)-infected participants must have well controlled HIV on antiretroviral therapy * Hepatitis B surface antigen (HBsAg) positive participants are eligible if they have received Hepatitis B Virus (HBV) antiviral therapy for at least 4 weeks and have undetectable HBV viral load * Participants with a history of Hepatitis C Virus (HCV) infection are eligible if HCV viral 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 transient ischemic 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 Multicentric Castleman's Disease * Received prior systemic anticancer therapy including investigational agents within 4 weeks before study intervention * Received prior radiotherapy within 2 weeks of start of study intervention, or has radiation-related toxicities, requiring corticosteroids * 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 infection requiring systemic therapy * Have not adequately recovered from major surgery or have ongoing surgical complications