Background and Aims: The risk of colorectal cancer (CRC) is increased among patients with inflammatory bowel disease (IBD). Based on a systematic and endoscopic follow up of patients with IBD at three University hospitals in Oslo, clinical and histological material has been available from patients at risk of CRC. The aim of the current study was to investigate age at diagnosis of IBD and the risk of developing CRC in this cohort of patients, adjusted for defined risk factors.
Methods: A cohort of patients with the diagnosis of IBD at three hospitals in Oslo prior to 2005, were matched against the CRC files of the Norwegian Cancer Registry. A patient control group (n=271) who did not develop CRC (n=66) was matched for date of birth, gender and years of follow up.
Results: Mean age at diagnosis of IBD was 28,9 years in patients with CRC and 32,0 years in patients without CRC (p=0,036). For every yearly increase in age at diagnosis of IBD, the risk of CRC was reduced by a factor of 0,933 (p<0,001). CRC was more likely to occur in patients with UC than CD (OR= 0,180, 95 % CI: 0,074-0,440, p<0,001). Number of colonoscopies and medical treatment were not significant risk factors of CRC.
Conclusions: In the present cohort, young age at diagnosis of IBD is a significant independent risk factor of CRC, adjusted for type of IBD. For every yearly increase in age, the risk of CRC decreases with a factor of 0,933. Consequently, odds of developing CRC are 50 % at the age of 10 years, 25 % at 20 years and 12,6 % at 30 years at diagnosis of IBD. This might have consequenses for surveillance strategies.