Immunotherapy for Digestive System Cancers: Progress, Challenges, and Future Directions

Immune checkpoint blockade has changed the management of several digestive system cancers, but its impact is highly context dependent. This review evaluates evidence for esophageal, gastric and gastroesophageal junction, colorectal, hepatocellular, biliary tract and gallbladder, and pancreatic cancers. Randomized phase III trials have established chemoimmunotherapy or dual-checkpoint strategies in advanced esophageal cancer, biomarker- and regimen-dependent first-line therapy in gastric cancer, PD-1-based therapy for MSI-H/dMMR colorectal cancer, atezolizumab–bevacizumab and STRIDE for unresectable hepatocellular carcinoma, and chemoimmunotherapy for advanced biliary tract cancer. Recent results also expand perioperative treatment: neoadjuvant checkpoint blockade produces high pathological response rates in dMMR colon cancer, adjuvant atezolizumab plus mFOLFOX6 improves disease-free survival in stage III dMMR colon cancer, and perioperative serplulimab improves event-free survival in PD-L1-positive resectable gastric cancer. These advances coexist with important negative findings. Pembrolizumab-containing therapy did not meet superiority end points in KEYNOTE-062, the initial adjuvant signal in IMbrave050 was not sustained, and unselected pancreatic ductal adenocarcinoma remains largely resistant to checkpoint blockade. Early vaccine, cellular, TIGIT, radiomics, spatial, and multi-omics studies remain hypothesis-generating and require external or randomized validation. Clinical interpretation should integrate evidence maturity, biomarker validity, immune-related toxicity, patient-reported outcomes, cost, access, and manufacturing demands rather than response rate alone.