Strong Pathologic Complete Response to Immunotherapy in MSI-High Esophagogastric Cancer

Immune checkpoint inhibitors have substantial activity across the spectrum of microsatellite-instability–high (MSI-H) cancers. Superior efficacy of these agents over chemotherapy was demonstrated recently for first-line treatment of MSI-H metastatic colorectal cancer. Recent studies also indicate high rates of clinical and pathologic complete response to anti-PD-1 therapy in locally advanced colon and rectal cancers. Investigators from France now report results from the GERCOR NEONIPIGA study, a single-arm phase 2 trial evaluating locally advanced MSI-H esophagogastric adenocarcinoma. Patients received preoperative therapy with ipilimumab given once every 6 weeks and nivolumab given every 2 weeks, both for 12 weeks total, followed by surgery, followed by another 9 months of weekly adjuvant nivolumab. Of the 32 patients enrolled, 72% were male, median age was 65, equal numbers had gastric and gastroesophageal junction primaries, 62% were cT3N+, and 22% had documented Lynch syndrome.

Among the 29 patients who went to surgery, the primary endpoint of achieving a pathologic complete response in 20% or more was reached (17 patients; 58.6%), and another 14% had <10% residual cancer found. Of three patients not going to surgery, two declined surgery but were documented to have a clinical complete response, and a third patient also achieving a clinical complete response was found on review of initial staging to have metastatic M1 nodal disease. R0 resection was achieved in 100% of operated patients. With the exception of one postoperative death, there were no recurrences in 31 patients. No new safety signals emerged.