This clinical trial is focused on studying treatments for gastroesophageal cancer, which includes types like gastric adenocarcinoma, gastroesophageal junction adenocarcinoma, and esophageal adenocarcinoma. The study will explore the effects of a combination of treatments, including a new drug called MK-2870, also known as sacituzumab tirumotecan, and an existing medication called pembrolizumab (also known as Keytruda). Additionally, various chemotherapy drugs will be used, such as capecitabine, fluorouracil, oxaliplatin, and calcium folinate. Other medications involved in the study include glucocorticoids, H2-receptor antagonists, antihistamines, and a combination of buclizine hydrochloride, paracetamol, and codeine phosphate.

The purpose of the study is to evaluate the safety and effectiveness of these combination therapies in treating gastroesophageal cancer. Participants will receive these treatments through different methods, such as oral use or intravenous infusion, which means the medication is given directly into a vein. The study will begin with a phase to ensure the safety and tolerability of the treatments, followed by an assessment of how well the treatments work in reducing the size of the cancer or stopping its growth.

Throughout the study, participants will be closely monitored for any side effects or adverse reactions to the treatments. The study aims to provide valuable information on the potential benefits and risks of these combination therapies for individuals with advanced gastroesophageal cancer. The trial is expected to continue until 2029, with recruitment starting in 2024.