Post-colonoscopy colorectal cancers (PCCRCs) account for up to 50% of colorectal cancers (CRCs) in patients with inflammatory bowel disease (IBD). We investigated characteristics of IBD patients with PCCRC and their survival.
We identified IBD patients (ulcerative colitis [UC] and Crohn’s Disease [CD]) diagnosed with CRC from 1995 to 2015. We defined PCCRC as diagnosed between 6 and 36 months, and detected CRC (dCRC) as diagnosed within 6 months after colonoscopy. We computed prevalence ratios (PRs) comparing PCCRC vs. dCRC and followed patients from the diagnosis of PCCRC/dCRC until death, emigration, or study end. Mortality was compared using Cox proportional hazards regression models adjusted for sex, age, year of CRC diagnosis, and stage. The main analyses focused on patients with UC.
Among 23,738 UC patients undergoing colonoscopy, we identified 352 patients with CRC, of whom 103 (29%) had PCCRC. Compared with dCRC, PCCRC was associated with higher prevalence of metastatic cancer (33% vs. 20%; PR: 1.64, 95% confidence interval [CI]: 1.13-2.38), cancers exhibiting mismatch repair deficiency (79% vs. 56%; PR: 1.40, 95% CI: 1.13-1.72), and proximally located cancers (54% vs. 40%; PR: 1.34, 95% CI: 1.06-1.69). The one- and five -year adjusted hazard ratios (HRs) of death for PCCRC vs. dCRC among UC patients were 1.29 (95% CI: 0.77-2.18) and 1.24 [95% CI: 0.86-1.79), respectively.
The characteristics of UC-related PCCRC suggest tumor biology as an important factor in the progression to cancer. However, the prognosis of PCCRC appears similar to that of dCRC.

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