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Breast cancer screening: Canadian guidelines put new emphasis on shared decision-making

By 8th August 2019No Comments

Updated Canadian guidelines on screening for breast cancer emphasizes shared decision-making between women and their doctors, supporting women to make an informed decision based on personal preferences when the balance between benefits and harms is uncertain.  (Klarenbach S et al. Recommendations on screening for breast cancer in women aged 40-74 years who are not at increased risk for breast cancer. CMAJ. 2018: 190(49):E1441. doi: 10.1503/cmaj.180463.)

Based on the latest evidence, including 29 studies assessing the value women place on anticipated benefits and harms from breast cancer screening, the guideline contains recommendations for women aged 40 to 74 years who are not at increased risk of breast cancer.

Breast cancer screening with mammography may reduce death from breast cancer, although it can also result in false positives, additional testing and possibly invasive procedures, as well as overdiagnosis, overtreatment and potential complications. Current evidence indicates a close balance between benefits and harms, leading to conditional recommendations based on patient preferences.


  • The task force charged with drawing up the guidelines recommends against screening women aged 40 to 49 years. This recommendation is conditional on the relative value a woman places on possible benefits and harms from screening. If women of this age prefer to be screened, they are encouraged to discuss options with their health care provider. Women in this age group face a higher risk of potential harms from false positives, overdiagnosis and overtreatment compared with other age groups, and the absolute benefit is smaller.
  • The task force recommends in favour of screening women aged 50 to 74 years with mammography every 2-3 years. This recommendation is also conditional as some women may choose not to be screened if they are concerned about overdiagnosis and the associated harms. The benefits of screening are from very low-certainty evidence indicating a modest reduction in the risk of death from breast cancer.
  • The task force recommends against screening with magnetic resonance imaging, tomosynthesis and ultrasonography in women not at high risk based on a lack of evidence.

In a related commentary, Dr. Deborah Korenstein, of Memorial Sloan Kettering Cancer Center  writes, “The new recommendations on breast cancer screening from the Canadian Task Force on Preventive Health Care serve as a model for the important role of guidelines in promoting value in health care.” Dr. Korenstein added  that, compared with other international guidelines, the task force’s guideline “is alone among similar guidelines in noting in the main recommendation for all age groups that ‘the decision to undergo screening is conditional on the relative value that a woman places on possible benefits and harms.’

doi: 10.1503/cmaj.180463.