Objectives: Colorectal cancers (CRCs) diagnosed relatively soon after a colonoscopy are referred to as interval CRCs. It is not clear whether interval CRCs arise from prevalent lesions missed at colonoscopy or represent specific aggressive biology leading to poor survival.
Methods: Using Danish population-based medical registries (2000-2009), we investigated patients with "interval" CRC diagnosed within 1-5 years of a colonoscopy, and compared them with cases with colonoscopy ≥10 years before diagnosis and to "sporadic" CRCs with no colonoscopy before diagnosis. Multivariate logistic regression was used to explore the association between clinical, demographic, and comorbidity characteristics and interval CRC. We assessed survival using Kaplan-Meier methods and mortality rate ratios (MRRs) using Cox regression, adjusting for covariates including the Charlson Comorbidity Index (CCI 0, 1-2, 3+).
Results: The comparison of the 982 interval CRCs to the 358 patients with CRC ≥10 years after colonoscopy revealed nearly similar characteristics and mortality. In the comparison with the 35,704 sporadic CRCs, interval cases were slightly older (74 vs. 71 years), more likely to be female (54 vs. 48%), have comorbidities (CCI3+: 28 vs. 15%), have proximal tumors (38 vs. 22%), and tumors with mucinous histology (9.1 vs. 7.0%), but stage was similar (metastatic 23 vs. 24%). In logistic regression analysis, female sex, localized stage at diagnosis, proximal tumor location, and high comorbidity burden were factors independently associated with interval CRC. The 1-year survival was 68% (95% confidence interval (CI): 65%, 71%) in interval and 71% (95% CI: 70%, 71%) in sporadic cases, with an adjusted MRR of 0.92 (95% CI 0.82, 1.0). After 5 years, survival was 41% (95% CI: 37%, 44%) in interval and 43% (95% CI: 42%, 43%) in sporadic cases, and the adjusted 2-5 year MRR was 1.0 (95% CI 0.88, 1.2).
Conclusions: Clinical characteristics and survival among interval CRCs did not suggest aggressive biology, but rather that the majority represented missed lesions.