If we assume that screening reduces breast cancer mortality by 15% and that overdiagnosis and overtreatment is at 30%, it means that for every 2000 women invited for screening throughout 10 years, one will avoid dying of breast cancer and 10 healthy women, who would not have been diagnosed if there had not been screening, will be treated unnecessarily. Furthermore, more than 200 women will experience important psychological distress including anxiety and uncertainty for years because of false positive findings. To help ensure that the women are fully informed before they decide whether or not to attend screening, we have written an evidence-based leaflet for lay people that is available in several languages on www.cochrane.dk. Because of substantial advances in treatment and greater breast cancer awareness since the trials were carried out, it is likely that the absolute effect of screening today is smaller than in the trials. Recent observational studies show more overdiagnosis than in the trials and very little or no reduction in the incidence of advanced cancers with screening.
Breast cancer screening with mammography: a population-based, randomized trial with mammography as the only screening mode.
A population-based, randomized breast cancer screening project was undertaken using mammography alone. Of 17,447 invited women aged 50-69, 12,765 (73%) attended the screening. On the basis of the screening films, malignancy was suspected in 405 women (3.2%) who were recalled for complete mammography. Additional films showed that the suspicion of malignancy was false in 194 women. The remaining 211 women (1.7%) were referred for clinical and cytological examination. Of these, 159 had surgery. Breast cancer was proved in 97 women, corresponding to a prevalence rate of 7.6/1000. Fifty-three (55%) of the carcinomas were either in situ or invasive with a diameter of less than or equal to 1 cm. Axillary metastases were found in 19 patients (19.6%). Cancers detected at screening were significantly less advanced than those in the control group. There was a remarkably high frequency of tubular carcinoma among cancers detected at screening.