Time to colonoscopy, cancer probability, and precursor lesions in the Danish colorectal cancer screening program

The aim of this study was to investigate the effect of response time from the Fecal Immunochemical Test (FIT) based screening invitation to the conclusive screening Optical Colonoscopy (OC) on the risk of detecting colorectal cancer (CRC), advanced stage disease and precursor lesions.

We used a cross-sectional study design and included all 62,554 screening participants registered in the Danish Colorectal Cancer Screening Database who tested FIT-positive between March 2014 and December 2016. The main exposure was response time, measured as the time from initial invitation to the conclusive OC. Our main outcomes were the probability of being diagnosed with CRC, advanced stage disease or precursor lesions.

Of the 62,554 FIT-positive participants, 53,171 (85%) received an OC and were eligible for analysis (median age 63.7 years, 56% men). In this group, 3,639 cancers were registered, 2,890 of which were registered with a defined stage of disease (79%), and 1,042 (36%) of these were advanced stage (UICC III & IV). In addition, 17,732 high-risk and 10,605 low-risk adenomas were identified. Compared to participants receiving the conclusive examination within 30 days, those receiving the examination more than 90 days after initial invitation were 3.49 times more likely to be diagnosed with any CRC (OR 3.49 [95% CI, 3.13-3.89]) and 2.10 times more likely to have advanced stage disease (OR 2.10 [95% CI, 1.73-2.56]). Those waiting for the longest were also more likely to have one or more high-risk adenomas (OR 1.59 [95% CI, 1.50-1.68]).

Increased screening response time was associated with a higher probability of detecting high-risk adenomas, any stage CRC and advanced stage cancer. More research is needed to explain what causes these associations.