Sex-Specific Outcomes after a Negative Colonoscopy in the Finnish Randomized Health Service Study during 2004 to 2016

In the randomized colorectal cancer screening trial carried out in Finland between 2004 and 2016, participants were referred to colonoscopy based on the results of the guaiac fecal occult blood test. We assessed sex-specific colorectal cancer incidence and standardized incidence ratios (SIR) after a positive guaiac fecal occult blood test and a negative colonoscopy.

We used data from a Finnish randomized colorectal cancer screening trial with colorectal cancer diagnoses from the Finnish Cancer Registry. We compared the colorectal cancer incidence of the colonoscopy-negative screening population with the expected incidence based on the control population in three follow-up periods ([0.5, 2), [2, 6), and more than 6 years) by calculating age- and sex-specific SIRs.

In men, the SIR was 0.28 [95% confidence interval (CI), 0.03-1.01] during the [0.5, 2) years of follow-up. During the [2, 6) years of follow-up, it was 0.51 (95% CI, 0.26-0.92), and during the 6 or more years of follow-up, it was 0.33 (95% CI, 0.12-0.72). In women, the SIRs were 1.63 (0.66-3.36), 1.15 (0.65-1.90), and 0.83 (0.40-1.52), respectively.

Unlike men, the negative colonoscopy was not associated with a lower incidence of colorectal cancer in any of the follow-up periods in women. This suggests that the guidelines for intervals between negative colonoscopy and the time of the next screening invitation might need to be considered separately based on sex.

This study emphasizes the difference in the protective effect of negative colonoscopy between men and women. More research is needed, especially in the context of new screening methods.