Validity of process indicators of screening for breast cancer to predict mortality reduction.

The aim of the study was to empirically assess the acceptable levels of process indicators as described in the European Community Guidelines using materials from the mammography service screening programmes. The Finnish programme was evaluated for effectiveness with a prior estimate of 0.74 for RR in Finland and 0.81 in Helsinki. Hence, the Finnish programme was likely to be somewhat less effective in terms of reduction in mortality than implied on the basis of early randomized trials, but probably approaching the same level of effectiveness. Finland therefore provides background data on the applicability of the process indicators that are indicators of performance and surrogates for effectiveness. The performance data on 10 Finnish screening centres at subsequent screens were used. These centres invited 687,000 women aged 50-64 years in 1991-2000. The mean compliance was 93% and the corresponding recall rate was 2.3%. The benign to malignant biopsy ratio was 0.43:1. The average breast cancer detection rate was 0.36%, 2.1 compared with the background incidence. The proportion of screen-detected stage II+ cancers was 26%. Most, but not all, of these process indicators met the desirable reference values of the European Community. The specific criteria of the European Community on stage distribution, rates of screen-detected cancers by stage and detection rate to background incidence may need reconsideration.