Rinatabart Sesutecan is an experimental medication being tested in this study. It is given through an intravenous infusion, which means it is delivered directly into a vein over a period of time. The drug is being studied as a single‑agent treatment (monotherapy) to see if it can shrink or stop the growth of advanced gastrointestinal cancers, such as colorectal, stomach, esophageal, pancreatic, and biliary tract cancers. Researchers are looking at how well the drug works against tumors and whether it is safe for patients.

PEGFILGRASTIM is a background medication used in the trial to support the patients’ blood cells. It is given as a subcutaneous injection (injected under the skin) and works by stimulating the body’s production of certain white blood cells, helping to reduce the risk of low blood counts that can occur during cancer treatment. This support allows patients to stay on the study therapy with fewer interruptions due to blood‑related side effects.

Metastatic colorectal cancer – This cancer starts in the colon or rectum and has spread to other parts of the body. Tumor cells can travel through the blood or lymph system to reach distant organs. As the disease progresses, new tumor sites may appear, increasing the overall tumor burden. The spread often leads to symptoms related to the affected organs. Monitoring the size and number of tumors helps assess disease activity.

Gastric and gastroesophageal junction cancer – This malignancy arises in the stomach lining or at the area where the esophagus meets the stomach. Cancer cells can grow outward, infiltrating nearby tissues and lymph nodes. Over time, they may extend into the abdominal cavity or spread through the bloodstream. The disease often presents with changes in appetite or digestion. As it advances, multiple tumor sites can develop.

Esophageal adenocarcinoma – This tumor originates from glandular cells in the lower part of the esophagus. It tends to grow inward, narrowing the esophageal tube and can extend into surrounding structures. Cancer cells may enter the lymphatic system and travel to distant organs. The disease can cause difficulty swallowing and weight loss as it expands. Continued growth leads to additional metastatic sites.

Pancreatic ductal adenocarcinoma – This cancer begins in the ducts that carry digestive enzymes within the pancreas. It typically infiltrates the surrounding pancreatic tissue and nearby blood vessels. Tumor cells can spread to the liver, lungs, or peritoneal cavity through blood or lymph channels. Early growth may cause vague abdominal discomfort. As it progresses, multiple organ involvement becomes common.

Biliary tract cancer – This malignancy develops in the bile ducts that drain bile from the liver to the intestine. The tumor can block bile flow and invade surrounding liver tissue. Cancer cells may travel to lymph nodes and distant organs such as the lungs. Disease advancement often results in additional tumor deposits throughout the abdomen.

Esophageal squamous cell carcinoma – This cancer originates from the flat cells lining the upper and middle parts of the esophagus. It grows outward, thickening the esophageal wall and can spread to nearby lymph nodes. Cancer cells may enter the bloodstream and form new tumors in distant sites. The disease frequently causes swallowing difficulties as it enlarges. Ongoing spread leads to multiple metastatic lesions.