Strongly Divergent Impact of Adherence Patterns on Efficacy of Colorectal Cancer Screening: The Need to Refine Adherence Statistics
Authors: Heisser Thomas , Cardoso Rafael , Guo Feng , Moellers Tobias , Hoffmeister Michael , Brenner Hermann 
Published: October 2020

AbstractObjectiveThe performance of colorectal cancer (CRC) screening programs depends on the adherence to screening offers. However, identical adherence levels may result from varying patterns of the population’s screening behavior. We quantified the effects of different adherence patterns on the long-term performance of CRC screening for annual fecal immunochemical testing (FIT) and screening colonoscopy at ten-year intervals.DesignUsing a multistate Markov model, we simulated scenarios where, while at the same overall adherence level, a certain proportion of the population adheres to all screening offers (‘selective’ adherence) or the entire population uses the screening offers at some point(s) of time, albeit not in the recommended frequency (‘sporadic’ adherence). Key outcomes for comparison were the numbers of prevented CRC deaths and prevented years of potential life lost (YPLL) after 50 simulated years.ResultsFor screening with annual FIT at adherence levels of 10-50%, ratios of prevented CRC deaths (YPLL) resulting from a sporadic versus a selective pattern ranged from 1.9-5.0 (1.9-5.0) for men and from 1.8-4.1 (1.8-4.3) for women, i.e. up to 4-5 times more CRC deaths and YPLL were prevented when the population followed a sporadic instead of a selective adherence pattern. Comparisons of simulated scenarios for screening colonoscopy revealed similar patterns.ConclusionAt the same overall level of adherence, ‘sporadic’ adherence patterns go along with much larger preventive effects than ‘selective’ adherence patterns. Screening programs should prioritize efforts to reach as many people as possible at least sporadically over efforts to maximize full adherence to repeat screening offers. Adherence statistics should be refined to better reflect ‘effective adherence’.What You Need to KnowBACKGROUND AND CONTEXTThe evidence on long-term effects of different patterns of longitudinal adherence (e.g. consistent or sporadic uptake) to colorectal cancer screening offers is limited.NEW FINDINGSIn a simulated hypothetical German population, at identical overall participation levels, large proportions of the population making sporadic use of screening offers were up to 4-5 times more beneficial to achieve sustained reductions of colorectal cancer mortality than small proportions of the population utilizing screening offers at the recommended frequency.LIMITATIONSThis study is limited by model simplifying assumptions and uncertainties related to input parameters.IMPACTEfforts to increase screening uptake should be concentrated on groups of consistent non-responders, e.g. by low-threshold screening offerings, such as directly mailed stool tests. Adherence statistics should be refined to better reflect “effective adherence”.SHORT SUMMARYThis simulation study demonstrates that commonly used adherence metrics for colorectal cancer screening do not sufficiently cover the effect of varying patterns of longitudinal adherence, which may considerably impact the long-term efficacy of screening programs.