Ileoanal Pouch Neoplasia in Familial Adenomatous Polyposis: An Underestimated Threat

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Abstract
Ileal pouch-anal anastomosis is one of the two main options available for the surgical treatment of patients with familial adenomatous polyposis. Its main advantage is the minimal risk of rectal cancer but a possible Achilles heel is the recurrence of epithelial neoplasia at the ileal pouch-anal anastomosis and within the ileal pouch. The significance of ileoanal anastomotic and ileal pouch adenomas is not yet fully appreciated, and there is a false sense of security about this operation. The consequences of worsening pouch polyposis are serious in that endoscopic treatment is unlikely to be an effective way of controlling it. This study has been done to alert those caring for patients with familial adenomatous polyposis to the looming danger of pouch polyposis and to suggest ways to deal with it. Studies reporting ileoanal pouch adenomas, ileal pouch-anal anastomotic cancers, and ileal pouch cancers in patients with familial adenomatous polyposis were reviewed. Reports of adenomas in Kock pouches and in Brooke ileostomies in the setting of familial adenomatous polyposis were included. The primary end points of the study were the time between pouch construction and the diagnosis of neoplasia, the age of the patients at the diagnosis of neoplasia, and the severity of the neoplasia. There were 18 studies reporting pouch neoplasia, 15 with adenomas, and 3 with cancer. Ten were case reports, five were retrospective studies, and three were prospective studies. All three prospective studies showed that the incidence of pouch adenomas increases with time of follow-up and that the severity of the polyposis varies. The median time from pouch construction to diagnosis of pouch adenomas was 4.7 years and the range was 0.5 to 12 years. There were six studies reporting eight patients with cancer at the ileal pouch-anal anastomosis, diagnosed a median of 8 years after pouch construction (range, 3-20 years). One-half of the cancers were locally advanced (T4) and one-half were not (T1 or T2). One-half followed stapled anastomosis and one-half were after mucosectomy. There were eight case reports of cancer described in an ileostomy in patients with familial adenomatous polyposis. The median time from ileostomy construction to the ileostomy cancers was 25 (range, 9-40) years. The combination of fecal stasis, adenomatous epithelium, and a germline APC mutation is a potent recipe for epithelial neoplasia. There is increasing evidence that this happens in an ileostomy but that the process is much faster in an ileal pouch. Endoscopic treatment of ileal adenomas is likely to be difficult, reducing the options for their control to excising the entire pouch or chemoprevention.