A global view of adherence to colonoscopy follow‐up in cascade screening of colorectal cancer

To overview the colonoscopy adherence in cascade screening of colorectal cancer (CRC) and evaluate potential influence of the initial tests based on an ecological evaluation.The performance of the initial screening tests and adherence to subsequent colonoscopy were extracted from relevant studies published up to 16 October 2020. The age-standardised incidence (ASRi) of CRC in populations in the year of screening was derived from the Cancer Statistics.One hundred sixty-six observational studies and 60 experimental studies were identified. Most studies applied cascade screening with faecal occult blood tests (FOBTs) as an initial test. The adherence to colonoscopy varied greatly across populations by continents, gross national income and type of initial tests, with a median (interquartile range) of 79.8% (63.1%-87.8%) in observational studies and 82.1% (66.7%-90.4%) in randomised trials. The adherence was positively correlated with the ASRi of CRC (r = 0.145, p = 0.023) and positive predictive value (PPV) of the initial tests (r = 0.206, p = 0.002) in observational studies and correlated with ASRi of CRC (r = 0.309, p = 0.002) and sensitivity of the initial tests (r = -0.704, p = 0.003) in experimental studies.Adherence to colonoscopy varies greatly across populations and is related with performance of the initial tests, indicating the importance to select appropriate initial tests.