Trials like the dostarlimab study in rectal cancer and NICHE in colon cancer show neoadjuvant immunotherapy can induce profound responses in MSI-high tumors. This is creating a new paradigm where major surgery might be avoided entirely for some patients, marking a significant shift in treatment strategy.

A modern strategy for localized MSI-high gastroesophageal cancer is to begin with dual immune checkpoint blockade. Clinicians can then perform an early response assessment and pivot to chemoimmunotherapy if the initial response is suboptimal, allowing for a flexible, response-adapted approach.

Experts favor a Nivolumab plus Ipilimumab (NIVO+EP) combination for newly diagnosed, MSI-high, stage IV gastroesophageal cancer patients who can tolerate it. This approach avoids chemotherapy and yields high, sustained response rates, including potential for complete pathologic responses in metastatic settings.

While immunotherapy is largely ineffective in metastatic microsatellite stable (MSS) colorectal cancer, emerging data suggests it may have surprising efficacy in the early-stage (neoadjuvant) setting. This differential response is likely due to a more favorable tumor microenvironment in earlier disease, suggesting a new therapeutic window.

Experts indicate that Tumor Mutational Burden (TMB) is losing relevance for guiding immunotherapy in GI cancers. The TMB cutoff of 10 is not considered reliable across tumor types, and clinicians still prefer combination chemo-immunotherapy even in TMB-high patients, unless MMR deficiency is also present.

Contrary to concerns about over-complicating treatment, experts advocate for fragmenting gastric cancer even further. The goal is to treat each molecularly defined subset as its own distinct disease, which requires deeper understanding and more targeted approaches rather than broad simplification.

Retrospective data suggests patients with MSI-high rectal cancer might not just respond poorly to standard neoadjuvant chemoradiation (TNT), but their disease could actually progress. This makes immunotherapy a potentially safer and more effective first-line neoadjuvant choice, not just an alternative.

The antibody-drug conjugate TDxD is a promising first-line therapy for HER2+ gastric cancer because of its bystander effect. The chemotherapy payload can kill adjacent HER2-low or negative cells, directly addressing the tumor heterogeneity that limits the efficacy of traditional HER2-targeted agents in this disease.

The COMET study found combining chemotherapy with atezolizumab did not improve overall survival versus atezolizumab alone. However, it nearly eliminated early progressive disease (2.8% vs. 32.4%), suggesting a critical role for patients with high tumor burden who cannot risk initial progression on monotherapy.