Unexpectedly High Incidence of Immune-Related Adverse Events in Gastric Cancer Patients Who Received Conversion Surgery After Nivolumab-Including Chemotherapy.

Background: Nivolumab-including chemotherapy (nivo-CTX) for stage IV gastric cancer (GC) may increase the chance of conversion surgery but risk of immune-related adverse events (irAEs) during perioperative period remains unclear. Methods: We examined irAEs in 36 patients with marginally resectable GC who received nivo-CTX followed by surgery between November 2021 and March 2024. Results: Marginally resectable factors were para-aortic lymph node in 23, liver in 3, esophageal intramural metastasis in 2, mediastinal lymph node in 1, peribiliary lymph node in 1, P1b in 2, Bulky N in 5, and T4b in 1. IrAE was observed in 12 patients (33.3%). Among 12 patients, irAE was detected during chemotherapy in 6 patients (50%), after chemotherapy to admission to surgery in 2 (16.7%), and after surgery in 4 (33.3%). Grade 2 irAE was found in 6 patients (16.7%); rash in 6 and thyroiditis in 2, grade 3 was in 3 (8.3%); adrenal insufficiency in 1, hepatitis in 1, and pituitary insufficiency in 1, grade 4 was in 3 (8.3%); type 1 diabetes mellitus in 2, pemphigus in 1, and encephalitis in 1. Grade 3 or 4 irAE was found in 6 patients (16.7%). Among the patients who had irAE, grade 3 or 4 was detected in 2 of 6 during chemotherapy (33.3%) but was in 3 of 4 (75%) after surgery. Conclusions: IrAE was frequently observed not only during chemotherapy but also during perioperative period. Surgeons must pay special attention to unfamiliar irAE events during perioperative period.