New breast cancer screening guidelines for women at average risk of breast cancer, published in CMAJ (Canadian Medical Association Journal), recommend no routine mammography screening for women aged 40-49 and extend the screening interval from every 2 years, which is current clinical practice, to every 2 to 3 years for women aged 50-74. The guidelines also recommend against routine clinical breast exam and breast self-examination in asymptomatic women.

The guidelines, aimed at physicians and policy-makers, provide recommendations for mammography, magnetic resonance imaging (MRI), breast self-exams and clinical breast exams by clinicians. They target average-risk women in three age groups (40-49, 50-69 and 70-74 years) who have not had breast cancer and do not have a family history of breast cancer in a mother, sister or daughter.

“As the Guideline on Breast Cancer Screening was last updated in 2001 and breast cancer screening has since become a subject for discussion amongst doctors and patients, the revitalized Canadian Task Force selected breast cancer screening as the topic for its first guideline,” said Dr. Marcello Tonelli, Chair of the Task Force on Preventive Health Care and Associate Professor at the University of Alberta, Department of Medicine, in Edmonton, Alberta. “We intend that this Guideline, which reflects the latest scientific evidence in breast cancer screening, be used to guide physicians and their patients regarding the optimum use of mammograms and breast examination.”

According to the guideline, outcomes of breast cancer screening such as tumour detection and mortality must be put into context of the harms and costs of false–positive tests, overdiagnosis and overtreatment. False–positive results can have a significant impact on the emotional well-being of patients and families. They can cause lifestyle disruptions and result in costs to both patients and the health care system.

“Providing Canadians with guidelines that reflect the most current scientific evidence is our priority,” said Dr. Tonelli. “We encourage every woman to discuss the risks and benefits of screening with their doctor before deciding on the best approach for them.”

“There was no evidence that screening with mammography reduces the risk of all-cause mortality,” state the authors. “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.”

In addition to the full guidelines, one-page information pieces are available for both physicians and patients on the task force website: http://www.canadiantaskforce.ca

The Canadian Task Force on Preventive Health Care is an independent body of 14 primary care and prevention experts. The task force has been established by the Public Health Agency of Canada to develop clinical practice guidelines that support primary care providers in delivering preventive health care.

In a related commentary, Dr. Peter Gøtzsche, Nordic Cochrane Centre, Copenhagen, Denmark, writes, “these guidelines are more balanced and more in accordance with the evidence than any previous recommendations.”

He states that evidence does not support mammography screening and argues that screening is ineffective and even harmful because diagnosis of cancers that would otherwise be undetected lead to life-shortening treatments and mastectomies.

“The main effect of screening is to produce patients with breast cancer from among healthy women who would have remained free of breast disease for the rest of their lives had they not undergone screening,” writes Dr. Gøtzsche.

“The best method we have to reduce the risk of breast cancer is to stop the screening program,” he concludes. “This could reduce the risk by one-third in the screened age group, as the level of overdiagnosis in countries with organized screening programs is about 50%.”

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Kim Barnhardt
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Canadian Medical Association Journal