New recommendations from the Canadian Task Force on Preventive Health Care advise against routine mammography screening for women aged 40 to 49 years and extend the screening interval from the current clinical practice of every 2 years for women aged 50 to 74 years to every 2 to 3 years (CMAJ. 2011;183[17]:1991-2001; www.cmaj.ca/content/183/17/1991.full.pdf+html). The guideline, which updates recommendations issued in 2001, are intended for application in average-risk women in their 40s, 50s, and 70s who have not had breast cancer and do not have a mother, sister, or daughter with a history of the disease.
The independent body of 14 primary-care and prevention experts concluded that the latest scientific evidence in breast cancer screening does not show that screening with mammography reduces the risk of all-cause mortality. In addition, they found that although screening might permit surgery for breast cancer at an earlier stage than diagnosis of clinically evident cancer—thus permitting the use of less invasive procedures for some women—available trial data suggest that the overall risk of mastectomy is significantly increased among recipients of screening compared with women who have not undergone screening.
The task force makes the following key recommendations:
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- Women aged 40 to 49 years should not undergo routine mammography because the risk of cancer is low in this group and the risks of false-positive results, overdiagnosis, and overtreatment are higher.
- Women aged 50 to 69 years should undergo routine screening with mammography every 2 to 3 years. A greater reduction in mortality is seen with mammography for women in this age group who are at average risk for breast cancer compared with similar women aged 40 to 49 years.
- Women aged 70 to 74 years should undergo routine screening with mammography every 2 to 3 years.
- Average-risk women should not undergo screening with magnetic resonance imaging (MRI), as there is no evidence that MRI screening reduces the risk of mortality or other clinically relevant adverse outcomes.
- For the same reason that MRI screening is not recommended, clinicians should not perform routine clinical breast examinations, nor should women perform breast self-examinations, to screen for breast cancer.
- When deciding whether to recommend mammography to a specific patient, clinicians should first discuss the tradeoff between benefits and harms as well as the patient’s values and preferences.
Overall, notes the task force, the reduction in mortality associated with screening mammography is relatively small for women aged 40 to 79 years at average risk of breast cancer.
