A case of gastric cancer with delayed onset of tumor reduction effect by nivolumab therapy.

Immune checkpoint inhibitors may have different clinical effects compared with conventional anticancer drugs. An 85-year-old male received chemotherapy for recurrent gastric cancer. As liver metastasis progressed, nivolumab was introduced as a fourth line treatment. Progression of liver metastasis in size was observed in CT after 3 courses of nivolumab therapy. Nivolumab treatment was discontinued, because the general condition of the patient also worsened. However, his general condition improved as hepatobiliary enzyme levels, inflammatory response, and tumor markers improved. Liver metastasis was shrinking on the image, so we resumed nivolumab therapy. To the authors' knowledge, this is the first case of pseudoprogression undergoing immunotherapy for gastric cancer. In this case, the antitumor effect was exhibited in a delayed manner and the tumor shrinkage was obtained.