Different phenotypes of gastric fundic gland polyposis and cancer in patients with familial adenomatous polyposis depending on Helicobacter pylori infection

A 37-year-old male with tarry stool presented to our hospital. Esophagogastroduodenoscopy revealed advanced gastric cancer, fundic gland polyposis (FGPsis), and negativity for Helicobacter pylori ( HP ) infection. Computed tomography exhibited multiple liver tumors. Total colonoscopy (TCS) demonstrated 139 tubular adenomas. He was diagnosed as having unresectable gastric cancer and received systemic chemotherapy. His sister and mother had colorectal adenomatous polyposis as revealed by TCS. His sister had FGPsis and was negative for HP infection, whereas his mother had early gastric cancer with HP infection but not FGPsis. Genetic analysis revealed a novel mutation in exon 15 of the APC gene (NM_000038.5: c.7647_7648_delTG) for the patient, his mother, and his sister, whereas no mutation was found for his father who had no gastrointestinal polyps. Therefore, the pedigree was diagnosed as an FAP family with a novel APC germline mutation which had different gastric phenotypes depending on the status of HP infection.