Evaluation of Overdiagnosis of Breast Cancer in Screening with Mammography: Results of the Nijmegen Programme

Abstract

Peeters P H M (Department of Epidemiology, Institute of Social Medicine, Nijmegen University, Verlengde Groenestraat 75, 6525 EJ Nijmegen, The Netherlands), Verbeek A L M, Straatman H, Holland R, Hendriks J H C L, Mravunac M, Rothengatter C, Van Dijk-Milatz A and Werre J M. Evaluation of overdiagnosis of breast cancer in screening with mammography: results of the Nijmegen programme. International Journal of Epidemiology 1989, 18: 295–299. After 12 years of screening for breast cancer in Nijmegen (1975–86), during which period six mammographic examination rounds were carried out, the extent of overdiagnosis was evaluated. Overdiagnosis is defined as a histologically established diagnosis of invasive or intraductal breast cancer that would never have developed into a clinically manifest tumour during the patient's normal life expectancy if no screening examination had been carried out. The whole 12-year period shows an excess of 11% of breast cancer cases in Nijmegen, compared with the neighbouring city of Arnhem, where no mass screening was performed. The incidence of breast cancers in Nijmegen in the period 1975–78 is higher, compared with the incidence rates in Arnhem; the rate ratio is 1.30. For the time-intervals 1979–82 and 1983–86 the rate ratios are 1.03 and 1.01 respectively with (0.89; 1.18) and (0.86; 1.16) as 95% confidence intervals. This leads to the conclusion that there is no evidence that screening programmes using modern mammography constitute a significant risk for over-diagnosis of breast cancers.