Post-colonoscopy colorectal cancers accounted for a substantial proportion of all IBD-related colorectal cancers. However, IBD patients had a low absolute risk of post-colonoscopy colorectal cancers1. These results from a Danish population-based cohort study were presented at the UEG Week 2020.
Post-colonoscopy colorectal cancers are defined as colorectal cancers diagnosed within 6-36 months following a colonoscopy. While post-colonoscopy colorectal cancers account for up to 8% of all colorectal cancers, they could account for up to 50% of all colorectal cancers diagnosed in patients with inflammatory bowel diseases (IBD). However, few studies have investigated the absolute risk in IBD-patients undergoing colonoscopy.
In almost 35,000 IBD patients who underwent colonoscopy, 138 post-colonoscopy colorectal cancers were found compared with 1,909 post-colonoscopy colorectal cancers among more than 350,000 non-IBD patients.
The 6-36 month cumulative incidence proportions of post-colonoscopy colorectal cancers after the first-time colonoscopy was 0.21% for IBD patients and 0.37% for non-IBD patients. The absolute risks were comparably low after subsequent colonoscopies for both IBD and non-IBD patients.
Comparing IBD with non-IBD patients, the hazard ratio of post-colonoscopy colorectal cancers after the first colonoscopy was 0.96, and the HRs after subsequent colonoscopies were also close to 1.0.
The 3-year rate of post-colonoscopy colorectal cancers was 24.3% for IBD patients (19.2% for patients with Crohn’s disease and 26.4% for patients with ulcerative colitis) compared with 7.5% for non-IBD patients.
Finally, the investigators calculated 3-year rates of post-colonoscopy colorectal cancers in IBD and non-IBD patients, stratified by the total number of colonoscopies performed during the study period. This rate was found to increase with the total number of colonoscopies performed for both IBD as well as non-IBD patients.
A better understanding of IBD-related post-colonoscopy colorectal cancer risk would improve patient guidance clinical decision making, and help foster the understanding of post-colonoscopy colorectal cancer development. As demonstrated in the current Danish study, post-colonoscopy colorectal cancers accounted for a substantial proportion of all IBD-related colorectal cancers on the one hand, but the absolute risk was low on the other hand.
An explanation for the high 3-year rates of post-colonoscopy colorectal cancers is an increased colonoscopy frequency in IBD patients, thereby increasing the likelihood that observed colorectal cancer is categorized as post-colonoscopy colorectal cancers.
1. Troelsen FS. Risk of a post-colonoscopy colorectal cancer diagnosis in patients with inflammatory bowel disease: a Danish population-based cohort study. UEG Week Virtual 2020, abstract OP027.