Time to screening in the systems of support to increase colorectal cancer screening trial

Understanding how interventions affect time to completion of colorectal cancer screening might assist in planning and delivering population-based screening interventions. The Systems of Support to Increase Colorectal Cancer Screening (SOS) study was conducted between 2008 and 2011 at 21 primary care medical centers in Western Washington. Participants in the study, ages 50 to 73 years, were eligible if they were enrolled in Group Health (Seattle, WA) and were due for colorectal cancer screening. Of note, 4,675 recruited participants were randomized to usual care or one of three interventions with incremental levels of systems of support for completion of colorectal cancer screening. We conducted time to screening analyses of the SOS data in years 1 and 2. We investigated whether these effects were time-varying. For year 1, the intervention effects on the time to completion of colorectal cancer screening were the strongest during the first two post-randomization months and then decreased, with no significant effect after the fifth month. For year 2, the intervention effects on the time to colorectal cancer screening increased from the first to the third month and then decreased, with no significant effect after the fifth month. Hence, each of the interventions to increase colorectal cancer screening had its greatest effect within the first 3 months after being offered to participants. Future studies should test whether booster interventions offered later could increase screening rate among those who remain unscreened. Additional research is needed to develop intervention strategies for colorectal cancer screening that focus on sustained behavior over time.