Background/Aims: This study investigated the occurrence of malignancies in Japanese patients with Crohn's disease (CD) and compared the incidence with that in the general population. Methods: The medical records of 294 CD patients, treated between 1989 and 2009, were reviewed and the prevalence of malignancies was assessed. Registration of person-years at risk was calculated individually, from the year of CD diagnosis until the year of cancer diagnosis, death or end of follow-up. The observed number of cancer cases was compared with the expected number, calculated on the basis of the individually computed person-years at risk and the corresponding age- and sex-specific incidence rates in the background population. Results: Thirteen cancers developed in 12 patients among a total of 4,248 person-years available for analysis. There were six CRCs, two gastric cancers, two uterine cancers, one small bowel cancer, one biliary cancer, and one cancer of unknown primary site. The risk of cancer (all sites) was significantly increased from that of the background population; SIR 2.24 (95% CI 1.19-3.83). In particular, the risk of CRC significantly increased in comparison to that of the background population; SIR 5.80 (95% CI 2.13-12.68). Conclusions: Japanese patients with CD are at increased risk of cancer, particularly CRC.
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