Printed in Great Britain Evaluation of Overdiagnosis of Breast Cancer in Screening with Mammography: Results of the

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 estab-lished 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 (0.88; 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. Since the Health Insurance Plan (HIP) trial in Greater New York1 several breast cancer screening programmes have been carried out all over the world. The results of the more recent ones such as the DOM-project in Utrecht,2 the Nijmegen screening project,3 the screen