IRA carries a definite cancer risk in FAP due to the remaining rectal stump [3,4], with a long-term rectal cancer risk reported to increase from 4% at 5 years to 25% at 20 years post-operatively . More recently it has been suggested that absolute patient age is the determinant factor for cancer development rather than the length of post-operative follow-up . This has led some to suggest that IRA should be converted to IPAA before the age of 50 . Several factors are thought to increase the rectal cancer risk with IRA, namely colorectal polyp density, and presence of col-orectal cancer at presentation, both of which are associated with higher proctectomy rates [8, 9]. Supporting this is the finding that having greater than 1000 adenomas in the colon is associated with double the risk of developing colorectal cancer . Other factors thought to increase colorectal cancer risk in the retained rectum include length of rectal stump
, age of patient at surgery , site of the APC mutation [8, 9] and adequacy of rectal surveillance
. Despite this, recent evidence does suggest a role for performing IRA in selected patients with FAP, namely those with relative rectal sparing (<10 adenomas), attenuated adenomatous polyposis coli or in adolescents and teenagers with mild polyposis coli [13, 14]. A study by Church et al. found IRA performed since 1983 (termed the "IPAA era") to carry a significantly lower rate of proctectomy for rectal cancer than those performed before 1983 (termed the "pre-IPAA era") . The authors attributed this to a greater number of patients in the IPAA era having undergone the procedure despite severe polyposis in order to avoid a permanent ileostomy in an otherwise young and asymptomatic patient. Although they demonstrated that careful selection of patients for IRA can result in a successful outcome, a limitation of the study was the significantly shorter length of follow-up in the IPAA era group. With restorative proctocolectomy and IPAA, although the incidence of adenomatous polyps in the ileal reservoir and the risk of malignant transformation is reduced, this cannot be eliminated [7, 16]. This is particularly the case with IPAA using stapled anastomosis where mucosectomy (as in the case of hand-sewn anastomosis) is not possible, and results in retained rectal mucosa with a potential to undergo adenomatous change [17-19]. Although both IPAA and IRA reduce the risk of colorectal cancer in FAP, neither completely remove this risk, resulting in a requirement for endoscopic surveillance.
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