Prediction of higher mortality reduction for the UK Breast Screening Frequency Trial: a model-based approach on screening intervals

BACKGROUND: The optimal interval between two consecutive mammograms is uncertain. The UK Frequency Trial did not show a significant difference in breast cancer mortality between screening every year (study group) and screening every 3 years (control group). In this study, the trial is simulated in order to gain insight into the results of the trial and to predict the effect of different screening intervals on breast cancer mortality. METHODS: UK incidence, life tables and information from the trial were used in the microsimulation model MISCAN–Fadia to simulate the trial and predict the number of breast cancer deaths in each group. To be able to replicate the trial, a relatively low sensitivity had to be assumed. RESULTS: The model simulated a larger difference in tumour size distribution between the two groups than observed and a relative risk (RR) of 0.83 of dying from breast cancer in the study group compared with the control group. The predicted RR is lower than that reported from the trial (RR 0.93), but within its 95% confidence interval (0.63–1.37). CONCLUSION: The present study suggests that there is benefit of shortening the screening interval, although the benefit is probably not large enough to start annual screening.