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Genetics of Colorectal Cancer (PDQ®): Genetics - Health Professional Information [NCI] - Major Genetic Syndromes

Table 5. Extracolonic Tumor Risks in Familial Adenomatous Polyposis continued...

Complicating the issue of differential diagnosis, FGPs have been increasingly recognized in non-FAP patients consuming proton pump inhibitors (PPIs).[64,67] FGPs in this setting commonly show a "PPI effect" consisting of congestion of secretory granules in parietal cells, leading to irregular bulging of individual cells into the lumen of glands. To the trained eye, the presence of dysplasia and the concomitant absence of a characteristic PPI effect can be considered highly suggestive of the presence of underlying FAP. The number of FGPs tends to be greater in FAP than that seen in patients consuming PPIs, although there is some overlap.

Gastric adenomas also occur in FAP patients. The incidence of gastric adenomas in Western patients has been reported to be between 2% and 12%, whereas in Japan, it has been reported to be between 39% and 50%.[68,69,70,71] These adenomas can progress to carcinoma. FAP patients in Korea and Japan are reported to have a threefold to fourfold increased gastric cancer risk compared with their general population, a finding not observed in Western populations.[72,73,74,75] The recommended management for gastric adenomas is endoscopic polypectomy. The management of adenomas in the stomach is usually individualized based on the size of the adenoma and the degree of dysplasia.

Level of evidence: None assigned

Duodenum/small bowel tumors

Whereas the incidence of duodenal adenomas is only 0.4% in patients undergoing upper gastrointestinal (GI) endoscopy,[76] duodenal adenomas are found in 80% to 100% of FAP patients. The vast majority are located in the first and second portions of the duodenum, especially in the periampullary region.[58,59,77] There is a 4% to 12% lifetime incidence of duodenal adenocarcinoma in FAP patients.[13,74,78,79] In a prospective multicenter surveillance study of duodenal adenomas in 368 northern Europeans with FAP, 65% had adenomas at baseline evaluation (mean age, 38 years), with cumulative prevalence reaching 90% by age 70 years. In contrast to earlier beliefs regarding an indolent clinical course, the adenomas increased in size and degree of dysplasia during the 8 years of average surveillance, though only 4.5% developed cancer while under prospective surveillance.[16] While this study is the largest to date, it is limited by the use of forward-viewing rather than side-viewing endoscopy and the large number of investigators involved in the study. Another modality through which intestinal polyps can be assessed in FAP patients is capsule endoscopy.[80,81,82] One study of computed tomography (CT) duodenography found that larger adenoma size could be accurately measured but smaller, flatter adenomas could not be accurately counted.[83]

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