S6331 Fundal Foveolar Adenomatous Polyposis in Gardner’s Syndrome: Is EUS a Good Option to Detect Invasion?

Introduction: Gardner syndrome (GS) is a subtype of familial adenomatous polyposis syndrome (FAP), a rare autosomal dominant condition involving mutation of the APC gene with near-complete penetrance and variable expressivity. GS is associated with both extensive intestinal polyposis and extra-intestinal manifestations. Nearly 10% of patients with FAP syndrome will develop gastric polyposis, and the risk of gastric cancer is about 0.6%. It is recommended that patients with FAP undergo upper endoscopy screening primarily for early detection of duodenal adenocarcinoma. The utility of endoscopic ultrasound (EUS) for the assessment of gastric polyposis in this population is not well established. We present a case of GS who underwent assessment for large adenomatous gastric polyps with dysplasia. Case Description/Methods: Fifty-nine-year-old woman with GS confirmed by genetic testing, with a history of total colectomy. She also has a positive family history of GS with gastrectomy for an unclear indication. She presented for yearly surveillance esophagogastroduodenoscopy (EGD) for gastric polyposis. It was noted that the largest polyp that was in the fundus had grown in size from 3 to 6 cm in 6 months. During the same time, the patient complained of increased symptoms of indigestion. EUS showed signs of submucosal invasion without muscularis propria involvement. A trial for en-block resection was unsuccessful. Histopathology examination showed fragments of foveolar polyps, and the immunohistochemical stain was negative for Helicobacter pylori. Computed tomography (CT) scan did not show significant peri-gastric lymphadenopathy. Given high-risk features, the decision was made to proceed with surgery. The patient underwent a total gastrectomy with a Roux-en-Y esophagojejunostomy. Histopathology showed innumerable polyposis with features of foveolar adenomas and low-grade dysplasia. Discussion: Gastric polyposis in GS can be difficult to assess properly. Nearly 50% of patients with FAP will develop foveolar dysplasia. However, the risk of progression to gastric cancer is low. Biopsies and standard polypectomy techniques seem to be suboptimal measures to rule out the development of adenocarcinoma. On the other hand, while EUS is recommended for the evaluation of gastric/duodenal submucosal lesions, its utility in mucosal-based gastric polyps is limited, and thus the interpretation of EUS findings in these patients should be interpreted carefully.