Summary
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.
The clinical course of Crohn's disease differs markedly over time, from ever-relapsing cases to a quiescent course with remission for several years, interrupted by years with relapse. No predictive factors have been found for the subsequent course with regard to age, sex, extent of disease at diagnosis, and treatment in the year of diagnosis. The relapse rate within the year of diagnosis and the following 2 years, however, does correlate positively (p = 0.00001) with the relapse rate in the following 5 years. Furthermore, the relapse rate for 1 year during the disease course influences the relapse rate the following year, indicating a disease pattern over time with waves of at least 2 years' duration. A slight tendency towards burning out was found. The disease course reflected in working capacity for the patients showed that a minor part--up to 15% after 15 years--will become incapable and obtain disablement pension, while 75% of the patients each year are fully capable of work. Within 10 years 50% of the patients will not have experienced any year with impaired capacity for work.
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