Impact of colorectal cancer screening participation in remote northern Canada: A retrospective cohort study

Screening provides earlier colorectal cancer (CRC) detection and improves outcomes. It remains poorly understood if these benefits are realized with screening guidelines in remote northern populations of Canada where CRC rates are nearly twice the national average and access to colonoscopy is limited.

To evaluate the participation and impact of CRC screening guidelines in a remote northern population.

This retrospective cohort study included residents of the Northwest Territories, a northern region of Canada, age 50-74 who underwent CRC screening by a fecal immunohistochemical test (FIT) between January 1, 2014 to March 30, 2019. To assess impact, individuals with a screen-detected CRC were compared to clinically-detected CRC cases for stage and location of CRC between 2014-2016. To assess participation, we conducted subgroup analyses of FIT positive individuals exploring the relationships between signs and symptoms of CRC at the time of screening, wait-times for colonoscopy, and screening outcomes. Two sample Welch t-test was used for normally distributed continuous variables, Mann-Whitney-Wilcoxon Tests for data without normal distribution, and Chi-square goodness of fit test for categorical variables. A P value of < 0.05 was considered to be statistically significant.

6817 fecal tests were completed, meaning an annual average screening rate of 25.04%, 843 (12.37%) were positive, 629 individuals underwent a follow-up colonoscopy, of which, 24.48% had advanced neoplasia (AN), 5.41% had CRC. There were no significant differences in stage, pathology, or location between screen-detected cancers and clinically-detected cancers. In assessing participation and screening outcomes, we observed 49.51% of individuals referred for colonoscopy after FIT were ineligible for CRC screening, most often due to signs and symptoms of CRC. Individuals were more likely to have AN if they had signs and symptoms of cancer at the time of screening, waited over 180 d for colonoscopy, or were indigenous [respectively, estimated RR 1.18 95%CI of RR (0.89-1.59)]; RR 1.523 (CI: 1.035, 2.240); RR 1.722 (CI: 1.165, 2.547)].

Screening did not facilitate early cancer detection but facilitated higher than anticipated AN detection. Signs and symptoms of CRC at screening, and long colonoscopy wait-times appear contributory.