ULCERATIVE-COLITIS AND CROHNS-DISEASE - A COMPARISON OF THE COLORECTAL-CANCER RISK IN EXTENSIVE COLITIS

The risk of developing colorectal cancer has been compared in two iden tically selected cohorts of patients with extensive Crohn's colitis (n =125) and extensive ulcerative colitis (n=486). In both groups the eff ects of selection bias have been reduced wherever possible. There was an is-fold increase in the risk of developing colorectal cancer in ext ensive Crohn's colitis and a 19-fold increase in risk in extensive ulc erative colitis when compared with the general population, matched for age, sex, and years at risk. The absolute cumulative frequency of ris k for developing colorectal cancer in extensive colitis was 8% at 22 y ears from onset of symptoms in the Crohn's disease group and 7% at 20 years from onset in the ulcerative colitis group. The relative risk of colorectal cancer was increased in both ulcerative colitis and Crohn' s disease among those patients whose colitis started before the age of 25 years. Whether the absolute risk is greater in the younger age gro up or merely reflects that the expected number of carcinomas increases with age is uncertain. While there is an increased risk of developing colorectal cancer in extensive colitis the number of patients with Cr ohn's disease who actually develop colorectal cancer is small because many patients with extensive Crohn's colitis undergo colectomy early i n the course of their disease to relieve persistent symptoms unrespons ive to medical treatment.