Expected long-term impact of screening endoscopy on colorectal cancer incidence: a modelling study

Abstract

BACKGROUND & AIMSScreening endoscopy reduces colorectal cancer (CRC) incidence but the time course and magnitude of effects beyond 10 years after screening are unknown. We aimed to estimate the expected time course and magnitude of long-term impact of screening endoscopy on CRC incidence.METHODSWe used Markov models based on the natural history of the disease along with data from the German national screening colonoscopy registry to derive the expected impact of screening colonoscopy at age 55 or 60 on cumulative CRC incidence according to time of follow-up over a period of up to 25 years.RESULTSAfter a single screening colonoscopy, cumulative CRC incidence is expected to be increased for approximately 4 to 5 years. This transient increase is expected to be followed by a steadily increasing reduction in cumulative CRC incidence for at least 25 years. Less than one third of this long-term reduction is expected to be seen within 10-12 years of follow-up, the length of follow-up reported on in RCTs on flexible sigmoidoscopy screening and in most cohort studies on both sigmoidoscopy and colonoscopy screening. In relative terms, risk reduction is expected to reach its maximum approximately 15 years after a single screening colonoscopy and 20-25 years after the initial screening colonoscopy in case of repeat screening colonoscopy after 10 years.CONCLUSIONSThe long-term impact of screening endoscopy on CRC prevention is expected to be much stronger than suggested by currently available evidence from RCTs and cohort studies with limited length of follow-up.

How long does it take until the effects of endoscopic screening on colorectal cancer mortality are fully disclosed?: a Markov model study

“…For CRC mortality, no initial increase occurs, and, as confirmed by our models, an even stronger reduction is expected, with relative mortality reduction after a single colonoscopy reaching its maximum already after 12–13 years. This is 2–3 years earlier than the maximum of relative reduction of cumulative incidence, which, according to our previous study is expected after 15 years …”

“…Previous studies on CRC incidence have shown that the protective effect of screening against CRC only became apparent after at least 4–5 years because of the detection of prevalent asymptomatic cancers at screening . While screening clearly does not prevent the occurrence of existing cases, these screen‐detected patients still benefit from early detection and timely treatment and have better chances of cure .…”

“…A multistate Markov model was set up to simulate the natural history of the adenoma–carcinoma process. The model structure has been described previously, and is outlined in Figure . A previously unscreened 55‐year‐old population enters the model with certain proportions of no neoplasm, nonadvanced adenoma, advanced adenoma and preclinical CRC, and the simulation starts from these proportions.…”

“…The proportions of no neoplasm, nonadvanced adenoma, advanced adenoma and preclinical CRC at the beginning of simulation (prior to screening) were calculated previously based on the data from 344,658 participants of the German screening colonoscopy program who had their first screening colonoscopy during 2003–2012 at the age of 55 years (Supporting Information Table S1). In brief, findings at screening colonoscopies (number, size and histological characteristics of polyps) as well as sociodemographic information are reported anonymously to the national screening colonoscopy registry. Participants were categorized according to the most advanced finding at screening colonoscopy into no neoplasm, nonadvanced adenoma, advanced adenoma or CRC.…”

Changes in colorectal cancer screening use after introduction of alternative screening offer in Germany: Prospective cohort study

“…In summary, despite these limitations, our study suggests that introduction of screening colonoscopy as an alternative screening offer in Germany increased adherence to CRC screening overall, with screening colonoscopy becoming the primary source for being up‐to‐date with CRC screening after 5–6 years. These encouraging results, along with model‐based projections, suggest that major reduction of CRC incidence and mortality is to be expected in the years and decades to come, which has already started to become evident in recent years and which could potentially be further enhanced by switching to an organized CRC screening program.…”