Mammography screening programs are widely employed in Europe and the United States. In the UK, all women over the age of 50 are invited for screening every three years as part of the NHS breast screening programme. Screening is carried out in order to detect breast cancer at an early stage, so that treatment can be started sooner when it is more likely to be effective. While early detection of breast cancer is beneficial, there are risks associated with screening that must be taken into account.
In an Opinion article published in BMC Medicine, Donella Puliti and Marco Zappa from the ISPO Cancer Prevention and Research Institute discuss whether breast cancer screening is effective based on the results of observational studies using different methodological approaches.
The authors discuss how results from case-control studies, which compare the screening history of women who have died from breast cancer with those who have not, show that mammography screening reduces breast cancer mortality. In accordance with case-control data, incidence-based mortality (IBM) studies also show clear benefits of screening. However, the results of some studies analyzing temporal trends in breast cancer mortality suggest that screening does not reduce the number of deaths. Puliti and Zappa describe the limitations associated with analyzing temporal trends, and indicate that results obtained from these studies should be interpreted with caution. They recommend that case-control and IBM studies are the most suitable approaches to assess the effectiveness of mammography screening, and conclude that it does reduce breast cancer mortality.
In line with Puliti and Zappa’s recommendation, a recent study found that at least seven lives are saved for every thousand women screened, suggesting that the risks are far outweighed by the benefits. Accordingly, the NHS breast screening programme is currently being extended to include women between the ages of 47 and 73.
However, whilst many believe that screening saves lives, some doctors are concerned that false positive results on mammography tests lead to unnecessary anxiety, and that needless treatment with unpleasant side effects may be given for slow-growing tumors. Some studies, such as the temporal trend analyses discussed by Puliti and Zappa, suggest that screening is not effective, and expert opinion is divided on the most appropriate study design to assess whether mammography does reduce deaths. This debate was highlighted during peer review of Puliti and Zappa’s article, and we look forward to seeing more articles discussing this interesting and controversial topic.