Canadian Task Force on Preventive Health Care shifts focus in updated guideline
An updated breast cancer screening guideline places a new emphasis on shared decision-making between women and their health care providers to support women to make an informed decision on based on preferences. The guideline, released by the Canadian Task Force on Preventive Health Care (Task Force), is published today in CMAJ (Canadian Medical Association Journal).
“In Canada, most women 50 years and older who are not at elevated risk are invited for mammography screening for breast cancer and face a decision about whether to participate,” said Dr. Ainsley Moore Vice-Chair of the Task Force. “The updated guideline shifts the focus to shared-decision making between women and their health care providers to decide whether to undergo screening or not based on their own values and preferences.”
Breast cancer screening using mammograms identifies breast cancer earlier and leads to a reduction in the risk of breast cancer mortality; however, it also leads to known harms including false positive results, further testing and possible breast biopsy, as well as overdiagnosis resulting in unnecessary treatment and potential associated complications. The most recent evidence examined by the Task Force continues to show a close balance between these potential benefits and harms.
“Shared decision making between patients and their physicians is increasingly emphasized in preventive health screening and these recommendations highlight the close balance between benefits and harms that warrant a shared decision making approach.” said Dr. Guylène Thériault, Assistant Dean, Distributed Medical Education, in the Department of Family Medicine, Faculty of Medicine, at McGill University. “The Task Force has made conditional screening recommendations to emphasize that women should be supported to make the decision that is most consistent with their own priorities regarding possible screening outcomes. For example, while screening is recommended in women aged 50-74, shared decision making should occur, and through this process some women will appropriately choose not to be screened.” said Thériault, who is also a member of the Task Force.
“The Canadian Partnership Against Cancer supports the Task Force’s recommendations on breast cancer screening, specifically the need for more informed conversations and shared decision-making between women and their health care providers,” said Dr. Craig Earle, vice-president, Cancer Control at the Partnership. “We know there are many women who have the positive experience of screening catching cancer early, but we know there are also some for whom screening resulted in unnecessary medical procedures and a stressful period waiting for results. The Partnership looks forward to continued work with provincial and territorial partners to monitor the performance of breast screening programs.”
The Guideline, developed by the Task Force, an independent body of primary care and prevention experts, examined the best and most current scientific evidence to formulate the recommendations on breast cancer screening.
While the Task Force has not changed the direction of its recommendations from its 2011 guideline, the new guideline clarifies recommendations as being conditional upon a woman’s personal priorities around harms and benefits of screening.
- The Task Force recommends against screening women aged 40 to 49 years old; the recommendation is conditional on the relative value a woman places on possible benefits and harms from screening. In situations where women of this age wish to be screened, they are encouraged to discuss options with their health care provider.
- The Task Force recommends in favour of screening women aged 50 to 74 years with mammography every 2-3 years. The decision to undergo screening is conditional on the relative value that a woman places on possible benefits and harms from screening. Clinicians are encouraged to engage in shared decision-making to support women to make an informed decision aligned with their priorities.
Current evidence continues to show a close balance between potential benefits and harms of breast cancer screening; this balance appears to be less favourable for women under 50 years of age. Individual women may differ in how they value these harms and benefits.
- The most important harm of screening is overdiagnosis which occurs when a woman is diagnosed with ‘breast cancer’ but the cancer would not have resulted in symptoms or harm in the woman’s lifetime. However, since doctors can’t tell which cancers will progress and which will not, the tendency is to treat them all. All cancer treatments (e.g., chemotherapy, radiation therapy, surgery) come with serious harms.
- For women aged 40 to 49 years who are not at increased risk of breast cancer, low-certainty evidence seems to suggest a small reduction in risk of breast cancer death. On the other hand, these women have a higher risk of potential harms, including false positive results, leading to further testing, possible breast biopsy as well as overdiagnosis resulting in unnecessary treatment and associated complications.
- For women 50 to 74 years who are not at increased risk of breast cancer, very low-certainty evidence suggests a modest reduction in the risk of breast cancer death. While potential harms of screening are lower than for younger women, they remain a concern.
- A review conducted for this guideline on women’s values and preferences about breast cancer screening suggests that many women aged 40 to 49 years would choose not to be screened if they were aware of outcomes for their age group. On the other hand, many women aged 50 years and older would choose screening given the more favourable balance of benefits and harms. Some women of this age may choose not to be screened based on their individual values and preferences around the benefits and harms of screening.
The Task Force noted that better-quality evidence is needed on the impact of breast cancer screening for women of all ages. Additional studies on Canadian women’s values and preferences for screening that are based on accurate estimates of both benefits and harms, conducted in a transparent and easily comparable manner, would help guide future recommendations.
About the Canadian Task Force on Preventive Health Care
The Task Force was established to develop clinical practice guidelines that support primary care providers in delivering preventive health care. The mandate of the Task Force is to develop and disseminate clinical practice guidelines for primary and preventive care, based on systematic analysis of scientific evidence.
Jennifer Field, H+K Strategies
December 10, 2018