Background and Aims: Studies implicating primary sclerosing cholangitis as a risk factor for colorectal neoplasia in patients with ulcerative colitis have been limited by small sample size and referral bias. The aim of this study was to determine the relative risk and cumulative incidence of colorectal neoplasia in a large sample of patients with sclerosing cholangitis. Methods: A sample of patients with primary sclerosing cholangitis (n = 178), stratified by geographic area of residence, was identified and followed up to determine survival and development of colorectal neoplasia. The relative risk of colorectal cancer was determined using age- and sex-specific incidence rates of colorectal cancer in the U.S. general population as well as rates in patients with ulcerative colitis from central Sweden. Results: The relative risk of colorectal cancer was elevated 10-fold (standardized morbidity ratio, 10.3; 95% confidence interval, 2.1- 30) compared with the general population for exposure to both sclerosing cholangitis and colitis but not cholangitis alone (standardized morbidity ratio, 4.9; 95% confidence interval, 0.1-27). The observed number of cancers was similar to that expected on the basis of rates in Swedish patients with ulcerative colitis. Conclusions: If primary sclerosing cholangitis is an additional risk factor for neoplasia in ulcerative colitis, the clinical significance of the risk seems to be low.
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