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

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Publication Date: 
Tue, 2012-07-17

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The Canadian Task Force on Preventive Health Care released its guideline on screening for breast cancer for average-risk women (aged 40 to 79) in late 2011. The guideline updated screening recommendations made by the Task Force’s predecessor, the Canadian Task Force on the Periodic Health Examination, in 2001. The focus of the guideline is on mammography screening, but the guideline authors also recommended against clinical breast examination (by physicians) and breast self-examination by patients. The Task Force issues guidelines for primary care (family) doctors on a range of preventive care issues. In this article, journalist Ann Silversides wades through the recent controversies about the guideline, explaining the issues and summarizing the evidence and current thinking about mammography screening. See also: Breast self-examination: What it means and why the thinking about it has changed.

By Ann Silversides


Photo: With permission from St David's HealthCare (Flickr).

The current debate about the value of mammography erupted last fall when the Canadian Task Force on Preventive Health Care released its recommendations for breast cancer screening for “average-risk women 40 to 74.”

The public wrangling has left women confused about what to do about mammography screening.

On November 22, 2011, the day after the recommendations were made public, a Toronto Star news story opened with the statement: “The mammogram wars have come to Canada.”

The “wars” refers to the firestorm of controversy in the United States when a similar U.S. task force had, in 2009, recommended against routine screening for women aged 40 to 49 years.

In the United States, this represented a radical change of policy. Previously, screening mammography had been recommended every one to two years for all women over 40.

But the Canadian position was not new. The Canadian Task Force on Preventive Health Care was repeating a recommendation—first made in 1994 and endorsed again in 2001—against routine screening for women 40 to 49 years old. It did, however, recommend routine screening for average risk women 50 to 69 years old every two to three years.

Organized breast cancer screening programs began in Canada in 1988 and are now in place in all provinces and territories except Nunavut. Most programs involve screening women 50 to 69 years old every two years, but British Columbia and Alberta invite women 40 and older into screening, although Alberta requires a doctor’s referral letter.

Even though the Task Force recommendation about who should be eligible for routine screening did not change, it provoked controversy and often hard-to-follow arguments. Technical debates based on statistics pit those who argue that formal screening programs should be expanded to younger women (on the basis that mammography benefits have been underestimated) against those who maintain that benefits have been exaggerated and harms downplayed. [See the series on these issues  and the position of the Canadian Breast Cancer Foundation on the screening debate].

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.”

But in Canada’s most populous province, Ontario, there are clear incentives to enroll women in screening. Family doctors are eligible for a $2,000 bonus if they enroll 80 per cent of their female patients aged 50 to 69 in a biannual mammography screening program.

One of the architects of Ontario’s performance target bonus system, which was introduced in 2001, is Dr. Ruth Wilson, former president of the College of Family Physicians of Canada.

She says the bonus incentive was based on evidence available at the time—strong evidence to support the benefits of mammography. Since then, there’s been accumulating evidence of harm from mammography.

“I think the performance target will have to change,” she says, adding however that it is difficult to “count or measure” if physicians have discussed pros and cons of a procedure with patients.

Still, new evidence must be taken into account. “Medicine is like that, says Wilson. “Many, many things have changed over the course of my lifetime. Things we fervently thought were right, turned out to be wrong, or things we thought were wrong turned out to be right.”  

In addition to the potential harms outlined earlier, new evidence is emerging that some small cancers, detected only through imaging, regress or disappear on their own.  

For this and other reasons, Dr. Steven Narod, a leading breast cancer researcher, notes that the benefit of screening is “greater for women with [lymph] node positive, than node negative breast cancer.” Node positive indicates that the breast cancer has spread to lymph nodes.  

A pamphlet from the Public Health Agency of Canada notes: “Even though your screening mammogram found breast cancer, your quality of life or the number of years you live may not change. Some breast cancers found by screening would otherwise cause no problems because women would die of something else first. These breast cancers could be slow growing cancers. So, if women with these cancers had not had screening, they might never have known they had cancer and would not have had treatment.”

Still, breast cancer screening programs are well entrenched—in 2008, 72 per cent of women 50 to 69 in Canada reported that they had had a mammogram in the previous two years, according to Statistics Canada.

"I think the public need to recognize that for noble and not-so-noble reasons, the health-care industry is always going to promote more, and the well-meaning will provide more since they are more afraid of missing a case than over finding too many cases,” says Steven Lewis, a health policy consultant and adjunct professor of health policy at Simon Fraser University.

Ann Silversides is an independent journalist and author who specializes in health policy.

Public discussion-debate “Is too much cancer screening hazardous to your health? The example of breast cancer”. A speech by Peter Gøtzsche, researcher and director of the Nordic Cochrane Centre. Published by Prescrire.

Book review of Mammography Screening: Truth, Lies and Controversy (Radcliffe Publishing, London/New York: 2012) by physician and researcher, Peter C. Gøtzsche. Available from the Centers for Medical Consumers website.

The Canadian Task Force on Preventive Health Care intends to create decision aids to help women decide whether or not to have a screening mammogram. In the meantime, two pamphlets to help with this decision making are available: the Public Health Agency of Canada pamphlet and the Cochrane Collaboration pamphlet.

Dr. Susan Love’s Breast Book (2010 edition) has an entire chapter outlining issues concerning breast cancer screening.

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