Postimaging Colorectal Cancer After Computed Tomography Colonography: A Danish Nationwide Study

Postimaging colorectal cancers (PICRCs) are defined by the World Endoscopy Organization as CRCs occurring more than 6 and up to 36 months after a negative colorectal imaging investigation (PICRC-3y). We calculated the absolute risk of PICRC among all participants who underwent computed tomography colonography (CTC) and estimated the proportion of all CRCs diagnosed after a CTC that could be classified as PICRC-3y.

We performed a nationwide study within the entire Danish population covering the period 2010-2020 with 2 aims. First, we followed patients from 7 months after their first-time CTC until the first PICRC occurrence, death, colectomy, emigration, or 36 months, and calculated 7- to 36-month cumulative incidence proportions for PICRC, as a measure of absolute risk. Second, we calculated PICRC-3y-rates by dividing the number of false-negative CTCs by the total numbers of true-positive and false-negative CTCs.

We identified 26,405 patients undergoing CTC, for whom the most likely indication (58%) was an incomplete colonoscopy within 3 months of the CTC. The 7- to 36-month cumulative incidence proportion for PICRC was 0.50% (95% confidence interval [CI]: 0.41%-0.61%) overall and 0.57% (95% CI: 0.44-0.72) for those with an incomplete colonoscopy. Based on 767 CTCs, the overall PICRC-3y-rate was 19% (95% CI: 16%-22%). The PICRC-3y-rate was 18% (95% CI: 15%-22%) for 491 (64%) cases with CTCs performed after an incomplete colonoscopy.

We found a higher overall PICRC-3y-rate than previously reported. The overall PICRC-3y-rate was also higher than reported 3-year rates for postcolonoscopy CRCs.