Most patients with familial adenomatous polyposis (FAP) develop gastric fundic gland polyps, with many displaying low‐grade dysplasia. This study evaluates the natural history and morphological phenotype of dysplasia in FAP‐associated fundic gland polyps.

Patients with FAP and dysplastic fundic gland polyps (n = 24) were identified. Twenty‐two of 24 FAP‐associated dysplastic fundic gland polyps showed a gastric phenotype and two had mixed phenotype. During a mean 6.1‐year follow‐up (range 0.8–12.6 years) and 5.7 endoscopies (range 2–22), one patient (4%) was diagnosed with a fundic gland polyp with high‐grade dysplasia, while 23 patients (96%) in this cohort had either no dysplasia or persistent low‐grade dysplasia. Contemporary patients with sporadic fundic gland polyps with low‐grade dyplasia had similar morphology and outcomes to the FAP‐associated fundic gland polyp cohort. Dysplasia in fundic gland polyps (FAP‐associated and sporadic) was associated less frequently with intestinal phenotype, high‐grade dysplasia and the finding of concurrent or subsequent carcinoma compared to contemporary patients with sporadic gastric dysplasia not occurring in fundic gland polyps.

This cohort of patients with FAP‐associated dysplastic fundic gland polyps rarely developed high‐grade dysplasia and gastric adenocarcinoma was absent.