Increased risk of large-bowel cancer in Crohn's disease with colonic involvement.

A cohort of 1655 patients with Crohn's disease diagnosed during 1983 in the Uppsala health care region, Sweden, was followed up with respect to the occurrence of colorectal cancer to the end of 1984. 12 colorectal cancers were diagnosed, yielding an increased overall risk of 2.5. The relative risk was similar for males and females. Duration of follow-up did not affect risk. Relative risk for disease of the terminal ileum only was 1.0; for terminal ileum and parts of colon 3.2; and for colon alone 5.6. Patients in whom Crohn's disease was diagnosed before age 30 with any colonic involvement at diagnosis had a higher relative risk (20.9) than those diagnosed at older ages (2.2).