Supportive care measures

The primary objective of the study is to compare sacituzumab tirumotecan combined with pembrolizumab to pembrolizumab alone with respect to overall survival (OS). The primary hypothesis is that the combination of sacituzumab tirumotecan and pembrolizumab is superior to pembrolizumab alone with respect to OS. All participants who have completed the first course of pembrolizumab may be eligible for up to an additional 9 cycles of pembrolizumab monotherapy if there is blinded independent central review (BICR)-verified progressive disease by Response Evaluation Criteria In Solid Tumors version 1.1 (RECIST 1.1) after initial treatment.

The goal of the study is to learn about the safety of Sacituzumab Tirumotecan and if people can tolerate it when given in the bladder and find the highest dose that people can take without having certain problems. Researchers will then choose a dose level of Sacituzumab Tirumotecan to use in future studies to learn how well the drug works.

Researchers want to learn if sacituzumab tirumotecan (MK-2870) alone or with other treatments can treat certain gastrointestinal (GI) cancers. The GI cancers being studied are either advanced (the cancer has spread to other parts of the body), or unresectable (the cancer cannot be removed with surgery). The goals of this study are to learn: * About the safety of sacituzumab tirumotecan alone or with other treatments and if people tolerate it * How many people have the cancer respond (get smaller or go away) to treatment