Gastric neoplasms in patients with familial adenomatous polyposis: endoscopic and clinicopathological features.

Abstract Background and Aims Gastric neoplasms in patients with familial adenomatous polyposis occur at a high rate and can cause death. The endoscopic findings of gastric neoplasms in these patients are characteristic, but not well recognized. To identify the relevant characteristics to enable early detection, we retrospectively investigated endoscopic findings of gastric neoplasms in patients with familial adenomatous polyposis, then compared the clinical, histopathological, and genetic features among subgroups. Methods Of 234 patients with 171 pedigrees at 2 institutes, 56 (24%) cases (133 gastric neoplasms) with 44 pedigrees were examined. Immunostaining was performed for histopathological evaluation by one blinded pathologist. According to the endoscopic findings, gastric neoplasms were divided into 4 types (L, UM-W, UM-T, and UM-R) and their clinicopathological features were examined. Results Of the cases, 93% could be classified into a single type. Among histological phenotypes, high-grade dysplasia was present in 26% (Type L), 41% (Type UM-W), 0% (Type UM-T), and 22% (Type UM-R). The immunological phenotype comprised the gastric type in 69% (93% in Type UM); it comprised the intestinal phenotype, including the mixed type, in 31% (61% in Type L). Moreover, 96% of the patients had concurrent duodenal neoplasms. Adenomatous polyposis coli gene status was identified in 93% of the patients; the pathogenic variant was detected in 98% but did not influence any endoscopic features. Conclusions Gastric neoplasms in patients with familial adenomatous polyposis were stratified into 4 types according to their endoscopic findings. The endoscopic phenotype was related to the histopathological phenotype, but not to germline variants.