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

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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.”