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.