OBJECTIVES : Current recommendations of The US Preventive Services Task Force on colorectal cancer

(CRC) screening strategies are based on models that assume 100% adherence. Since adherence can largely

affect screening outcomes, we aimed to compare the effectiveness of CRC screening strategies under

reported adherence rates. Our modeling highlights the importance that adherence plays on the effectiveness of

any screening program.

METHODS : We developed and validated an individual-level simulation model to assess the effectiveness of

colonoscopy (COL), flexible sigmoidoscopy (FS), high-sensitivity guaiac fecal occult blood test (HS-gFOBT),

fecal immunochemical test (FIT), multitarget stool DNA test (FIT-DNA), computed tomography colonography

(CTC), and methylated SEPT9 DNA test (SEPT9) in terms of CRC incidence and mortality, incremental lifeyears

gained, number of colonoscopies, and adverse events.

RESULTS : Assuming 100% adherence, FIT-DNA, FIT, HS-gFOBT, and SEPT9 averted 58-59 CRC cases and 28

CRC deaths; COL and CTC strategies 56 cases and 27 deaths, while FS averted 39 cases and 19 deaths per

1,000 individuals. Life-years gained were similar across FIT-DNA, FIT, HS-gFOBT, SEPT9, CTC, and COL

strategies. Number of colonoscopies was highest with COL (3,567), followed by SEPT9 (3,231), HS-gFOBT

(2,584), FIT-DNA (2,079), FIT (2,067), CTC (1,691) and FS (1,538). Assuming reported adherence, SEPT9

averted 54 CRC cases and 26 CRC deaths, followed by COL with 49 cases and 24 deaths, and FIT-DNA, FIT,

CTC and HS-gFOBT with approximately 36-41 cases and 18-21 deaths averted per 1000 individuals screened.

Life-years gained reflected the effectiveness of each strategy in reducing CRC cases and deaths.

CONCLUSIONS : Adherence has a substantial impact on screening outcomes and may influence selection of

optimal screening strategies.