Sex-specific outcomes after a negative colonoscopy in the Finnish randomized health service study in 2004-16.

In the randomized colorectal cancer (CRC) screening trial carried out in Finland between 2004 and 2016, participants were referred to colonoscopy based on the result of fecal occult blood test (gFOBT). We assessed sex-specific CRC incidence and standardized incidence ratios (SIR) after a positive gFOBT and a negative colonoscopy. We used data from a Finnish randomized CRC screening trial with CRC diagnoses from the Finnish Cancer Registry. We compared the CRC incidence of the colonoscopy-negative screening population to 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% CI: 0.03 to 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 to 0.92) and 6 or more years 0.33 (95% CI: 0.12 to 0.72). In women, the SIRs were 1.63 (0.66 to 3.36), 1.15 (0.65 to 1.90), and 0.83 (0.40 to 1.52), respectively. Unlike men, the negative colonoscopy was not associated with a lower incidence of CRC in any of the follow-up periods in women. This suggests that the guidelines for intervals between negative colonoscopy and the time of next screening invitation might need to be considered separately based on sex. This study emphasizes the difference of protective effect of negative colonoscopy between men and women. More research is needed, especially in the context of new screening methods.