Evaluation by Markov chain models of a non-randomised breast cancer screening programme in women aged under 50 years in Sweden.

STUDY OBJECTIVE: To apply Markov chain models that have previously been used on data in randomised trials of breast cancer screening to data from an uncontrolled service screening programme; to compare results with those from a randomised trial. DESIGN: A service screening programme in Uppsala county, Sweden, inviting 25,660 women aged 39-49 to mammographic screening every 20 months, and the Swedish Two-County Trial inviting 19,844 women aged 40-49 to two yearly screening, compared with 15,604 women of the same age in an unscreened control group. Data were analysed using Markov chain models and quasi- likelihood estimation procedures. MAIN RESULTS: The results with respect to parameters of disease progression were very similar between the two studies. Use of estimated progression rates to predict the effect on mortality ranged from a 10% to a 17% reduction in breast cancer mortality in the Two-County Study and predicted a 15% reduction in the Uppsala programme. These compare well with the observed mortality reduction of 13% in the Two-County Trial. CONCLUSIONS: The screening in the Uppsala programme is likely to have a similar effect to that observed in the Two-County Trial. It is feasible to evaluate non-randomised service screening programmes using Markov chain models.