Here we presented a 44 yr old male patient with an abdominal pain who had a distal gastric adenocarcinoma in his endoscopic biopsy. The pathology reported a chromogranine negative, CK20-positive, PD-L1 5% positive adenocarcinoma with MLH1 (-)and PMS-2(-) MSI status. PET/CT showed enlarged gastric wall (SUVmax 23.99) and enlarged perigastric lymphadenopathy (SUVmax 22.03) and no distant metastasis.

The patient received 4 courses of Nivolumab plus FLOT-4 chemoimmunothrapy in neoadjuvant setting. He experienced Grade 2 myelotoxicity and 2 packages of red blood were transfused. Following 4 courses of chemoimmunotherapy a total gasterectomy was performed and the pathology reported no evidence of tumor in the stomach and also perigastric lymph-nodes revealing a pathological complete response.

There has been no standart treatment for MSI-high gastric cancer, yet. Very few phase I-II studies wth limited number of patients suggest an immunotherapy-based treatment.

Here we report a combination regimen of original FLOT-4 chemotherapy with an PD-L1 Ab (nivolumab) that resulted a pCR in the neoadjuvant setting. Four courses of the same chemotherapy was planned in the adjuvant setting.