A simple method to estimate the episode and programme sensitivity of breast cancer screening programmes

Background: The estimation of breast cancer screening sensitivity is a major aim in the quality assessment of screening programmes. The proportional incidence method for the estimation of the sensitivity of breast cancer screening programmes is rarely used to estimate the underlying incidence rates. Methods: We present a method to estimate episode and programme sensitivity of screening programmes, based solely on cancers detected within screening cycles (excluding breast cancer cases at prevalent screening round) and on the number of incident cases in the total target population (steady state). The assumptions, strengths and limitations of the method are discussed. An example of calculation of episode and programme sensitivities is given, on the basis of the data from the IMPACT study, a large observational study of breast cancer screening programmes in Italy. Results: The programme sensitivity from the fifth year of screening onwards ranged between 41% and 48% of the total number of cases in the target population. At steady state episode sensitivity was 0.70, with a trend across age groups, with lowest values in women aged 50-54 years (0.52) and highest in those 65-69 (0.77). Conclusions: The method is a very serviceable tool for estimating sensitivity in service screening programmes, and the results are comparable with those of other methods of estimation.