Gastric Cancer Showing Partial Response 10 Months after Administration of Nivolumab

We report on a case of Stage IV gastric cancer in which a primary lesion showed a complete response and a target lymph node showed partial response (PR) 10 months after the administration of nivolumab. An 80-year-old woman complained of anorexia. Esophagogastrodoudenoscopy revealed type 3 gastric cancer. Biopsy specimens were classified as Group 5, poorly-differentiated adenocarcinoma. CT examination showed an enlarged #11 lymph node (LN) and swelling of #16a2 LN. PET/CT showed accumulation in the primary lesion and #2 LN. We diagnosed it as cT4aN3cM1(LYM) cStage IV. Though we performed chemotherapy with S-1 plus oxaliplatin as the 1st-line therapy, the adverse events and disease progression lead us to 2nd-line therapy with ramcirumab plus paclitaxel. As it also showed progressive disease (PD), we administered nivolumab as the 3rd-line therapy. Though the primary lesion shrunk, biopsy was Group 1, #11 LN enlarged slightly after 6 courses. It was very hard to judge whether we should continue administration of nivolumab or not, but we decided to continue, as her clinical symptoms and QOL were remarkably improved. We diagnosed PR after 19 courses as #11 LN shrunk markedly. Primary lesion showed scar formation, biopsy was classified as Group 1 again, and #11 LN shrank furthermore after 30 courses. She had been given nivolumab at that time. We believe this was a delayed response to nivolumab. Our findings suggest that there are cases of gastric cancer with delayed onset of tumor reduction effect through the administration of nivolumab.