Study to Assess the Efficacy and Safety of Rina-S in Participants With Advanced Gastrointestinal (GI) Cancers

Key Inclusion Criteria: • All study cohorts * Participant has histologically or cytologically confirmed GI cancer. * Participant has documented metastatic or unresectable disease, not amenable to treatment with curative intent. * Participant has measurable disease per the Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 at baseline. * Participant must have radiological disease progression while on or after receiving the most recent regimen. * Participant has Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. * Participant has life expectancy ≥3 months. * Participant must be able to provide a newly obtained or archival tissue sample. * Participant must have adequate organ and bone marrow function, per laboratory test results prior to Rina-S administration. Key Exclusion Criteria (all study cohorts): * Participant has clinically significant non-malignant gastrointestinal disorders, including but not limited to, diarrhea \> grade 1, ulcerative colitis, inflammatory bowel disease. * Participants with recent (up to 4 weeks) history of significant gastrointestinal bleeding, current cancer related ulcerations, fistula, abscess or recent perforation (within 4 to 6 weeks). * Participant has a past or current malignancy other than the inclusion diagnosis before the planned first dose of trial treatment, or any evidence of residual disease from a previously diagnosed malignancy. * Participants with newly identified or known unstable (eg, progressing brain metastases) or symptomatic central nervous system (CNS) metastases or history of carcinomatous meningitis (also known as leptomeningeal disease). * Prior treatment with topoisomerase-1 inhibitor containing antibody-drug conjugate (ADC). * Treatment with an anticancer agent within 28 days prior to the first dose of trial treatment. Note: Other protocol-defined Inclusion and Exclusion criteria may apply.