This last story focuses on how women and policy makers must balance the benefits and harms of screening mammography.
The issues raised in this series are relevant to screening for other diseases, such as PSA for prostate cancer.
The Canadian Task Force on Preventive Health Care recently issued recommendations about screening mammography for women at average risk of breast cancer. For women between 40 and 49 years of age, the Task Force recommended against screening. For women older than 50 years, they recommended screening every 2 to 3 years. The Task Force characterised both of these recommendations as “weak.”
The reason the Task Force gave for the difference in recommendations is that the risks of harm from regular screening mammography were felt to outweigh the benefits in most women under 50, but the benefits were felt to outweigh the harms in most women over 50.
The harms of screening mammography estimated by the Task Force are shown in the infographic below.
The importance of individual choice
Much has been written against and in support of the Task Force recommendations. Some have criticized the Task Force of under-estimating the benefits of screening mammography because they claim newer mammography technology will detect more treatable cancers. Others have suggested that the benefits of screening mammography were exaggerated because most of the improvement in deaths from breast cancer has been due to better treatment, not earlier detection.
The Task Force concluded that screening mammography in average risk women likely reduces the risk of dying from breast cancer. However, they note that, depending on the women’s age, between about 450 and 2100 women need to be screened for 11 years to prevent one death from breast cancer.
As well, some women who undergo screening mammography will have an unclear test result which will require further tests, some women will undergo biopsies that turn out not to find cancer, and others will have some cancers treated unnecessarily with surgery, radiation and chemotherapy.
Are the harms of an indeterminate or false positive mammogram worth it, to prevent a death from breast cancer?
Weighing the evidence
The relevant emphasis placed upon the benefits and harmsof screening mammography will vary from woman to woman. As Shelagh McRae, a family doctor on Manitoulin Island has pointed out, the impact of repeated testing might be quite different for someone in rural Ontario who has to drive many hours back and forth to appointments than for someone who lives in a big city.
Many argue that primary care physicians must provide women with accurate information about screening and support them in informed decision making about whether they wish to undergo screening mammography. However, the ability for primary care providers and patients to have accurate and detailed conversations about screening can be limited by time and other factors.
A dedicated screening mammography program is a population-level choice
In contrast to the individual-based decision making described above, organized screening programs generate general guidance for broad age categories, and provide simple messages encouraging screeening. These screening programs use approaches like educating health care providers about the benefits of screening for their patients, providing financial incentives to practitioners to achieve screening targets, and public education campaigns aimed at women and advising them to have a regular mammogram.
Dedicated screening programs consume limited public resources which could be used on other health care priorities. Therefore, it is important to ensure that these programs provide good value. In many ways this is a more difficult decision than an individual woman’s choice about mammography because policy makers are forced to make a decision that applies to a broad population.
It is much more difficult politically to stop a screening program once it is in place, than to decide not to institute one in the first place. Steven Lewis, a health policy expert in Saskatchewan noted that screening mammography programs were first developed decades ago when the evidence was different than it is now. He argues that based on current evidence, screening programs would likely not be instituted. However, Lewis also suggests that most governments wouldn’t want to face the backlash of ending an existing program.
Ontario has a population-wide screening mammography program focused on women aged 50 to 69. Given what is known about the benefits and harms of screening mammogrpahy in women of average risk, should Ontario stop the screening program altogether, provide additional information to women about the benefits and harms of screening mammography, more aggressively advertise screening or maintain the status quo?