Mammography screening: Weighing the pros and cons for women’s health

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Publication Date: 
Tue, 2012-07-17

Women in North America “have been taught to be terrified of breast cancer,” says Dr. Cornelia Baines, a leading breast cancer researcher and co-investigator of the Canadian National Breast Screening Study and follow up studies.
Yet it is lung cancer—not breast cancer—that is the leading cause of cancer death in women. According to the 2011 Canadian Cancer Statistics report from the Canadian Cancer Society, lung cancer accounted for an estimated 9,300 deaths of Canadian women in 2011, while breast cancer accounted for 5,100 deaths.
“Most women who get breast cancer don’t die from it,” Baines explained in an interview. And while breast cancer accounts for five to 10 per cent of deaths among Canadian women, a far greater proportion (about 41 per cent) of women die from cardiovascular and related diseases. This includes myocardial infarction, ischemic heart disease, arrhythmias, high blood pressure and stroke, according to the Heart and Stroke Foundation of Canada.
As well, mortality from breast cancer is declining for a variety of reasons including better treatment, and earlier detection due to public awareness, as women spot symptoms and visit doctors much earlier than in the past.

To be clear, mammography screening—the subject of the Task Force recommendations—is when women, without any symptoms of breast cancer, “participate on a routine basis to have mammograms done to find breast cancer at an early stage,” according to the Public Health Agency of Canada.

This type of mammogram looks for signs that breast cancer may be developing in women who have no apparent reasons for concern. It is distinct from diagnostic mammography, usually done to check for breast cancer because a woman has some apparent symptom.

Many people are confused by this distinction and may not be aware that women who are not part of a screening program are eligible for mammography with a doctor’s referral. For example, in Ontario in 2010—where the screening program is for women 50 and older—fully 181,644 women aged 40 to 49 had mammograms. Over the same time period, 351,167 women over 50 had mammograms in Ontario.

Eligibility policies for screening mammography now differ significantly by province. In British Columbia women are eligible to enroll in that province’s screening program from age 40 without a doctor’s referral, while a doctor’s referral is necessary for women under 50 to be enrolled in the Alberta Breast Cancer Screening Program.

The term “average risk” in the Task Force recommendations means that the recommendations do not apply to women with factors that place them in a higher risk category, such as having a close female relative who has (or had) breast cancer.

And although this point got lost in most of the media coverage and controversy, the Task Force emphasizes the need for health-care providers to discuss with all women the benefits and harms associated with mammography as well as the patient’s values and preferences.

“There’s been a lot of emphasis on the potential benefits of mammography in any age group,” said Dr. Marcello Tonelli, co-author of the Task Force’s 2011 recommendations on breast cancer screening. “We tried to refocus that to say, yes, there are benefits and there are also potential harms, and women need to be aware of both in order to make an informed decision.”

Potential harms considered by the Task Force focus on over-diagnosis of breast cancer which can lead to additional imaging, biopsies and procedures, distress and other psychological responses, and additional radiation exposure from mammograms. According a recent Norwegian study, 15 to 25 per cent of cancer cases are over-diagnosed, which means that for every 2500 women invited for screening, 6 to 10 women are over-diagnosed. The risks posed by radiation from mammography, and the possible contribution to increased rates of breast cancer, have not been adequately studied according to some experts.

“Effective communication about overdiagnosis of breast cancer will require great care—and evaluation to determine how best to do it; otherwise, women may become fearful or angry. Just because communicating with patients will be difficult does not mean that we should not tackle this problem. Informed women deserve no less when deciding about breast cancer screening” (p. 537).
Elmore, J. G and Fletcher, S.W. (2012). Overdiagnosis in breast cancer screening: Time to tackle an underappreciated harm [Editorial]. Annals of Internal Medicine, 156(7):536-537.

Mammograms are more difficult to read in younger women, says Baines.

The Task Force is recommending a performance target to ensure that family doctors discuss the pros and cons of mammography with their female patients, Tonelli said.

“If you have a technology or intervention that has no side effects and no downside, then sure, let’s go ahead and screen,” said Tonelli. “But where the benefits and harms are similar in magnitude or where things like mastectomies, having breasts removed unnecessarily, enter into the equation, we think women should have the opportunity to discuss those.”

With screening, he said, “you’re starting out with healthy people so we really need to inform them and treat them like adults as opposed to being paternalistic, especially in this area.”

To that end, Tonelli explained that the Task Force will work on providing doctors and women with tools to help with decisions—“not just throw numbers at them, but work with decision aids, and graphics.”

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