Review article: the risks of malignancy from either immunosuppression or diagnostic radiation in inflammatory bowel disease.

Inflammatory bowel disease is associated with an increased risk of gastrointestinal malignancy. There has been concern that either diagnostic medical radiation and long-term drug therapy--particularly immunosuppression--might contribute to this increased cancer risk. For the major drug groups (5-aminosalicylates, steroids and immunosuppressants) data are scant but broadly reassuring. Only azathioprine (including 6-mercaptopurine) has been investigated at all carefully. Short- to medium-term therapy probably poses a very slightly increased risk of malignancy which is easily accepted given the current limitation of this agent to second-line use. Continuous therapy for more than two years is much less well documented, and caution should be maintained. A hypothetical model based on data from occupational radiation exposure has been constructed; this permits reasonable confidence that the medical use of ionising radiation contributes a negligibly increased risk of malignancy overall, and is particularly unlikely to add significantly to the incidence of gastrointestinal malignancy.