Cancer characteristics, prognoses and mortality of colorectal cancer in patients with Crohn's disease - A Danish nationwide cohort study, 2009-2019.

Background/aims: Investigate the impact of Crohn's Disease (CD) on patient- and cancer characteristics and mortality in patients with colorectal cancer (CRC).

Methods: A nationwide cohort study of patients diagnosed with CRC in Denmark from January 1st 2009 to December 31st 2019. Cancer characteristics were retrieved from the Danish Colorectal Cancer Group registry and merged with a nationwide cohort for inflammatory bowel disease. The main outcome was all-cause mortality in CRC patients with and without CD, comparing CD patients with CRC with CRC in the general population, evaluated by adjusted Cox regression analysis and propensity score-matching.

Results: Of 38 077 CRC patients, 245 (0.6%) had CD. The median age at cancer diagnosis was 69 years (interquartile range (IQR): 60-76) for CD-CRC and 71 years (IQR: 64-78) for non-CD CRC (p<0.001). Most cancers were located in the right colon in the CD-CRC group. CD was not associated with increased all-cause mortality in the cohort overall. CD patients with colon and rectal cancer and UICC stage III tumors had a higher mortality rate in multivariate- (hazard ratio (HR) 1.60 (confidence interval (95%CI)1.13-2.27), p=0.008) and univariable analyses (HR 1.57 (1.11-2.22), p=0.011). In the propensity score-matched analysis, CD was not associated with increased mortality for colon (HR 1.06 (0.82, 1.36), p=0.7) or rectal cancer (HR 1.25 (0.79, 1.98) p=0.3).

Conclusion: This nationwide study identified distinct features of colon and rectal cancer in patients with CD that have implications for the timing of diagnoses, disease course and mortality specifically in UICC stage III disease.