External Validation of a Colorectal Cancer Model Against Screening Trial Long-Term Follow-Up Data

The University of Sheffield School of Health and Related Research (ScHARR) Bowel Cancer Screening Model has been used previously to make decisions about colorectal cancer screening strategies in England.

The objective of this study was to perform an external validation of the ScHARR model against long-term follow-up data about colorectal cancer (CRC) incidence and mortality reductions due to screening, from the Nottingham trial of guaiac faecal occult blood testing for CRC, and the UK Flexible Sigmoidoscopy Screening Trial.

The ScHARR model was adapted prior to validation to reflect the setting of each trial in terms of population characteristics, details of screening and surveillance programs, uptake of screening, and further investigations and study follow-up. The impact of using current versus historical CRC incidence and mortality data in the validation was also examined by carrying out a series of analyses in which historical data from different years was included in the model.

The ScHARR model was able to predict CRC incidence and mortality rate/hazard ratios from both trials to well within the 95% confidence intervals in the observed data. While it was less accurate in predicting absolute incidence and mortality rates, modeling historical incidence and mortality data enabled these predictions to be improved considerably.

The ScHARR model is able to replicate the long-term relative benefit from screening observed in 2 large-scale UK-based screening trials and can therefore be considered to be an appropriate tool to facilitate decision making around the English bowel cancer screening program.