Potential for prevention: a cohort study of colonoscopies and removal of adenomas in a FIT-based colorectal cancer screening programme.

Introduction: Evidence suggests that colorectal cancer (CRC) screening using guaiac faecal occult blood tests (gFOBT) reduces the CRC burden by facilitating timely removal of adenomas. Yet, the faecal immunochemical test (FIT) is being implemented in many countries. The aim of this study was to analyse the risk of having adenomas detected when invited for FIT-based screening as compared to those not yet invited. Material and Methods: The study was designed as a register-based retrospective cohort study. The potential for prevention was estimated as number of individuals who had no adenomas, non-advanced adenomas, and advanced adenomas detected per 1000 invited/not yet invited individuals and the relative risk (RR) of each of the three outcomes. Results: A total of 1,359,340 individuals were included, 29.6% of whom had been invited and 70.4% had not yet been invited to participate in CRC screening. Compared with the not yet invited population, the invited group had a RR of no adenomas of 2.28 (2.22-2.34) and a RR of advanced adenomas of 7.41 (6.93-7.91). The RR of colonoscopy was 2.93 (2.87-2.99) for the invited population compared with the not yet invited population. Conclusion: The RR of having a colonoscopy was three times higher among those invited compared to those not yet invited for CRC screening and twice as often those who had been invited compared to those not yet invited had no adenomas detected. Still, the risk of advanced adenomas was more than seven times higher among the invited population, indicating that the screening programme holds great potential for reducing the CRC burden.