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

Abstract

Introduction Colorectal cancer (CRC) is one of the leading causes of cancer morbidity and mortality worldwide. A recent randomized trial has suggested persisting protection from CRC incidence and mortality of a single flexible sigmoidoscopy for up to 17 years and possibly beyond. We performed a simulation study to explore the time course and magnitude of protection provided by screening colonoscopy against CRC death over 25 years. Methods Using data from the German national screening colonoscopy registry, a multi-state Markov model was set up based on the adenoma-carcinoma pathway to estimate the cumulative CRC mortality when different proportions of the population have a single screening colonoscopy at age 55, or two screening colonoscopies at ages 55 and 65. Ratio and difference of the expected cumulative CRC mortalities among screened and unscreened populations were calculated over follow-up to reflect the impact of screening colonoscopy. Results Cumulative CRC mortality continuously increased with age, and in the absence of screening reached 2.6% and 1.7% at age 80 for men and women, respectively. A single colonoscopy at age 55, even with limited uptake, was predicted to lead to much lower cumulative mortality (0.7% and 0.5% for men and women, respectively at age 80 when uptake was 100%). Relative mortality reduction continued to increase over more than 10 years and reached the maximum around 12–13 years after screening. Although relative risk reduction became attenuated for even longer periods of follow-up, absolute risk reduction steadily increased throughout follow-up and more than 70% of the total risk reduction was observed between 13–25 years. A repeat colonoscopy 10 year later further enhanced the effects and the cumulative mortality remained at 0.1% to 0.2% throughout follow-up when uptake was 100%. Conclusions Even a single (once only) screening colonoscopy has the potential to prevent most of CRC mortalities. Protective effects are expected to be long lasting and to become fully manifest after more than two decades from screening.