We herein report a rare case of hereditary diffuse gastric cancer in a Japanese man. A 41-year-old man underwent esophagogastroduodenoscopy which revealed a small gastric erosion. Biopsy specimens showed signet ring cell carcinoma, and endoscopic submucosal dissection was performed. The patient's elder sister had died of gastric cancer at 38 years old. Considering the family history, a genetic test was conducted and revealed a CDH1 germline mutation. Although no carcinomatous lesion was detected endoscopically, prophylactic total gastrectomy was performed. The resection specimen showed seven microlesions of signet ring cell carcinoma confined to the lamina propria mucosae.
Keywords: CDH1; endoscopic submucosal dissection; hereditary diffuse gastric cancer; prophylactic gastrectomy; signet ring cell carcinoma.