A case of multiple metastatic gastric cancer with primary lesion vanished after administrating nivolumab, and the effect remains even after discontinuance of therapy.

Nivolumab is one of the immune checkpoint inhibitors available for chemotherapy-resistant gastric cancer. There have been few reports of confirmed prominent shrinkage of the primary tumor and some reports of prolonged antitumor effect after discontinuance of the drug, but it is not universal. A 67-year-old male was admitted to our hospital and diagnosed with metastatic gastric cancer that had spread to the bilateral lobe of the liver, distant lymph nodes, and peritoneum. He received five courses of S-1 plus oxaliplatin, followed by three courses of ramucirumab plus paclitaxel leading to disease progression. Then, the patient was administered nivolumab as third-line therapy. Tumor size was markedly reduced after three courses, esophagogastroduodenoscopy (EGD) revealed scar formation on the lower gastric corpus after seven courses, and biopsy specimen showed no malignancy. When a slight lower limb muscle weakness manifested, possibly an immune-related adverse event (irAE) after 15 courses, we stopped administration of nivolumab. The patient has survived for 26 months since his first visit, and elimination of the primary tumor and ascites with noted shrinkage of liver and lymph node metastases have followed for more than 10 months since discontinuance of nivolumab.