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

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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

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 HealthyDebate.ca 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.