[A Case of Pseudo Progression during SOX+Nivolumab Therapy for Unresectable Gastric Cancer].

A 78-year-old male presented with circumferential stenosis in the gastric antrum and was diagnosed with signet cell carcinoma via biopsy. Contrast-enhanced CT revealed cT4aN0M0, cStage ⅡB, and he was referred to our department for surgery. Although pylorus-preserving gastrectomy was initially planned, extensive pancreatic invasion led to the decision for an unresectable diagnosis, and a gastrojejunostomy was performed instead. Approximately 1 month postoperatively, SOX plus nivolumab therapy was initiated without adverse events, resulting in stable disease(SD)after 12 courses over 10 months. After 13 months(15 courses), the patient experienced vomiting, diagnosed as gastrojejunostomy stenosis due to peritoneal dissemination. Given poor performance status, the patient transitioned to best supportive care(BSC). During follow-up, the patient gradually resumed oral intake. Ten months after discontinuing SOX plus nivolumab therapy, a CT scan showed primary tumor reduction and disappearance of peritoneal dissemination nodules, suggesting pseudo progression. The patient declined further surgery or chemotherapy and remains under outpatient observation.