Medical Research: What are the main findings of the study?
Dr. de Glas: It remains unclear whether mass breast cancer screening has a beneficial effect in older women. In the Netherlands, the upper age limit of the breast cancer screening program was extended from 69 to 75 years in 1998. If a screening program is effective, it can be expected that the incidence of early stage tumours increases, while the incidence of advanced stage tumours decreases. The aim of this study was to assess the incidence of early stage and advanced stage breast cancer before and after the implementation of mass screening in women aged 70-75 years in the Netherlands. We showed that the extension of the upper age limit to 75 years has only led to a small decrease of advanced stage breast cancer, while the incidence of early stage tumours has strongly increased. For every advanced stage tumour that was prevented, 20 “extra” and early stage tumours were diagnosed.
Medical Research: Were any of the findings unexpected?
Dr. de Glas: These findings were to some extend unexpected, as previous observational studies showed beneficial effects of breast cancer screening in terms of survival outcomes. However, it must be noted that these previous studies often suffered from lead time bias, length time bias and selection bias, which may explain the discrepancy between these studies and the present study.
Medical Research: What should clinicians and patients take away from your report?
Dr. de Glas: Since we have shown that each “prevented” advanced stage tumour resulted in 20 “extra” and therefore overdiagnosed early stage tumours, this implies that mass screening in women aged 70-75 leads to a considerable proportion of overdiagnosis. Overdiagnosis and overtreatment could have a great impact on quality of life and physical function of older breast cancer patients, as they are at increased risk of adverse outcomes of breast cancer treatment. Consequently, unfavourable effects of screening may outweigh the benefits from a certain age. Moreover, the additional costs of treating overdiagnosed tumours could result in a tremendous increase in health expenditure due to the screening program, while no actual health benefits are being obtained.
Medical Research: What recommendations do you have for future research as a result of this study?
Dr. de Glas: We propose that routine breast cancer screening in women over the age of 70 should not be performed on a large scale. Instead, the harms and benefits of screening should be weighed on a personalized basis, taking remaining life expectancy, breast cancer risk, functional status and patients’ preferences into account.