Longitudinal Surveillance of Gastric Polyposis in Familial Adenomatous Polyposis: Incidence, Progression, and Endoscopic Outcomes

BACKGROUND: Gastric manifestations of familial adenomatous polyposis (FAP) have traditionally been considered of limited relevance in Western populations, with surveillance focused on duodenal disease. Recent data suggest that progressive gastric polyposis, particularly in the proximal stomach, may be associated with dysplasia and carcinoma. We aimed to characterize longitudinal gastric phenotype evolution and compartment-specific risk in a contemporary Western FAP cohort. METHODS: We conducted a retrospective longitudinal cohort study of patients with genetically confirmed FAP undergoing structured upper gastrointestinal surveillance between 2019 and 2023. Gastric phenotypes were assessed separately for the fundus/corpus and antrum. Fundic gland polyp (FGP) burden was recorded semiquantitatively. Gastric dysplasia and carcinoma were analyzed as compartment-specific outcomes. RESULTS: A total of 299 patients (1281 upper endoscopies; mean follow-up 2.6 years) were included. Fundic/corpus polyposis was present in 81.9% of patients at the baseline. During follow-up, the FGP burden increased substantially, with more than 100 polyps observed in 52.2% of patients during their 5th-year follow-up. Fundic/corpus dysplasia increased from 10.7% at baseline to 40.0% (annual point prevalence) by year 5 and was independently associated with a baseline FGP burden > 200 polyps. Gastric adenocarcinoma occurred in 6 patients (2.0%), predominantly in the proximal stomach and in the setting of extensive polyposis, with poor outcomes. In contrast, antral dysplasia followed a more indolent course. DISCUSSION: In FAP, gastric disease is dynamic and compartment-specific. Progressive fundic gland polyposis is associated with a high-risk phenotype for proximal gastric neoplasia, supporting phenotype-driven gastric surveillance strategies.