Moderators of the effectiveness of an intervention to increase colorectal cancer screening through mailed fecal immunochemical test kits: results from a pragmatic randomized trial

Background Colorectal cancer (CRC) screening rates remain suboptimal, particularly in low-income and underserved populations. Mailed fecal immunochemical testing (FIT) may overcome common barriers to screening; however, the effect of mailed FIT kits may differ across important subpopulations. The goal of the current study was to examine sociodemographic and health-related factors that moderate the effect of an intervention of automated direct mail of FIT kits at health clinics serving low-income populations. Methods This study is a secondary analysis of the Strategies and Opportunities to Stop Colon Cancer in Priority Populations (STOP CRC) study, a cluster-randomized pragmatic trial to increase uptake of CRC screening in patients seen at federally qualified health centers. The intervention involved tools embedded in the electronic medical records to enable participating clinics to mail FIT kits and related materials to eligible participants. We examined the rate of FIT completion by potential moderating characteristics using electronic health record data supplemented by the American Community Survey and the Centers for Medicare & Medicaid Services Geographic Variation datasets, linked via geocoding to patients' addresses. All patients aged 50-75 seen in participating health clinics who were eligible for CRC screening were included. Results Although not always statistically significant, we saw a consistent pattern of increased FIT return rates among intervention participants compared to control participants across all subgroups studied, with incidence rate ratios (IRRs) generally ranging from 1.25 to 1.50. FIT completion in the intervention group ranged from 15 and 20% across subpopulations, typically three to six percentage points higher than the control group participants. The only moderator with a statistically significant interaction was race: persons of Asian descent showed a twofold response to the intervention (adjusted incidence rate ratio [aIRR] = 2.06, 95% confidence interval 1.41 to 3.00). Conclusions Response to a mailed FIT intervention was generally consistent across a wide range of individual and neighborhood-level patient characteristics, including typically underserved patients and those in low-resource communities.