Evaluation of the effect of breast cancer screening by record linkage with the cancer registry, the Netherlands

Objective-To evaluate the effect of a breast cancer screening programme by record linkage with the cancer registry. Setting-Breast cancer screening programme in mid- and southern Limburg, the Netherlands. Method-The data files of the breast cancer screening programme and the Maastricht Cancer Registry were linked in order to evaluate the effect of breast cancer screening. Only the first primary breast tumour was included in the evaluation. Results-From 1990 until 1995 90001 women participated in the first round of the breast cancer screening programme and 64 637 in subsequent rounds. After the introduction of screening the annual number of breast cancer diagnoses increased by almost 50%. The incidence decreased to previous levels after completion of the first screening round. Record linkage detected 219 interval cancers (within two and a half years of a screening), a proportionate incidence of 31% in the first year and 60% in the second year of the two-year interval between screenings. The incidence of node positive breast cancer was 1% lower in 1994 and 15% lower 1995 than the incidence in the period 1987-90. Conclusions-Evaluation of the effect of breast cancer screening in the Netherlands can be performed using routinely available cancer registry data. The results of this evaluation seem promising, but further studies are necessary to find ways to reduce the incidence of interval cancer.