Population-based colorectal cancer screening by fecal immunochemical testing over multiple rounds

Colorectal cancer (CRC) is one of the major causes of death in the Netherlands, accounting for over 5100 deaths in 2015. Population screening aims to detect CRC or its precursors, advanced adenoma, in an early phase, thereby reducing CRC morbidity and mortality. A recent observational study demonstrated a 22% reduction in CRC mortality from screening with a fecal immunochemical test (FIT). FIT-based screening is a two-step screening strategy in which all individuals with a positive FIT are referred for colonoscopy, the reference standard for the detection of CRC and adenomas. FIT-based screening can only be effective if there is a willingness to participate and perform the FIT, as well as to subsequently undergo colonoscopy if FIT-positive.
In the Netherlands, a national screening program for CRC, based on biennial testing with a single FIT, is gradually being implemented since January 2014. Before the implementation of the national program, two FIT-based CRC screening pilot programs were initiated. Since 2006, these two pilot programs have been inviting approximately 27,000 persons for biennial FIT screening. In 2014, these two cohorts were combined and invited for a fourth pilot round of screening. Following this ‘forerunner group’ by continuing biennial FIT screening enabled us to obtain data over multiple screening rounds, and to anticipate the future results of the Dutch national program. The research reported in this thesis covers a number of issues concerning four rounds of FIT-based CRC screening within this ‘forerunner group’ and aimed to evaluate the effectiveness of FIT-based CRC screening, in order to further optimize the screening strategy. We evaluated participation rates and adherence over multiple screening rounds, compared FIT-based screening to endoscopy screening, and studied cancers not detected within the screening program.