[A case of AFP-producing gastric cancer with peritoneal metastasis treated effectively with chemotherapy, mainly using S-1 and trastuzumab].

A 71-year-old man, diagnosed with advanced gastric cancer and severe pyloric stenosis, was introducted to our hospital. Para-aortic lymph nodes metastasis and pancreas invasion were seen with enhanced CT scan. Serum AFP showed a high price (1,465.3 ng/mL). Because significant peritoneal metastases were seen in the abdominal cavity, gastrojejunostomy was performed. Overexpression of the HER2 gene was seen by immunostaining for peritoneal dissemination of the omentum. After starting S-1 + CDDP + trastuzumab, the AFP was normalized immediately (7. 6 ng/mL). We then performed colostomy for a sigmoid colon stenosis. S-1 + DOC + trastuzumab was administered afterward, and we performed closure of the colostomy because the stenosis was improved. Macroscopic peritoneal dissemination in the abdomen disappeared. AFP-producing gastric cancer with peritoneal metastasis has a poor prognosis, but chemotherapy, mainly with S-1 and trastuzumab, was effective for it.