Although colorectal cancer (CRC), complicating ulcerative colitis and Crohn's disease, only accounts for 1–2% of all cases of CRC in the general population, it is considered a serious complication of the disease and accounts for approximately 15% of all deaths in inflammatory bowel disease (IBD) patients.
The magnitude of the risk was found to differ, even in population-based studies. Recent figures suggest that the risk of colon cancer for people with IBD increases by 0.5–1.0% yearly, 8–10 years after diagnosis. The magnitude of CRC risk increases with early age at IBD diagnosis, longer duration of symptoms, and extent of the disease, with pancolitis having a more severe inflammation burden and risk of the dysplasia-carcinoma cascade.
Considering the chronic nature of the disease, it is remarkable that there is such a low incidence of CRC in some of the population-based studies, and possible explanations have to be investigated. One possible cancer-protective factor could be treatment with 5-aminosalicylic acid preparations (5-ASAs).
Adenocarcinoma of the small bowel is extremely rare, compared with adenocarcinoma of the large bowel. Although only few small bowel cancers have been reported in Crohn's disease, the number was significantly increased in relation to the expected number.