Controversy over new mammogram guidelines continues
Published Friday, November 25, 2011 9:07AM EST
TORONTO - The release this week of revamped Canadian breast cancer screening guidelines has set off a war of words between those who support the recommendations and those who predict that following them will lead to more women dying of the disease.
Caught among all the rhetoric are women themselves. And what are they to think -- and more importantly, to do?
The most vociferous criticism of the guidelines developed by the Canadian Task Force on Preventive Health Care is focused on its direction to average-risk women in their 40s. The expert panel advises against routine mammography in this age group, saying that potential harms arising from the test trump the possible benefit of a small reduction in deaths.
Those harms include false-positive results requiring repeat tests, biopsies and in some worst-case scenarios, unnecessary mastectomies, radiation and chemotherapy. A review of international clinical trial evidence, on which the guidelines are based, shows a third of women will have a false-positive.
The task force determined that 2,100 women would have to be screened every two to three years over an 11-year period to prevent one breast cancer death.
"What I take away from the number is if you are a woman 40 to 49, if you and 999 other women go for screening, no one in the group will see a life saved," said task force chair Dr. Marcello Tonelli of the University of Alberta. "You need to have a group of 2,100 before you'd save a life.
"And looking around the room, one in three of you would have a false positive result ... and one in 30 of you would have a biopsy that you didn't need. And some of you would have an unnecessary mastectomy, or breast removed, or chemotherapy."
But Dr. Nancy Wadden, chair of the mammography accreditation program for the Canadian Association of Radiologists, contends the guidelines are based on studies from 25 to 40 years ago, using outmoded mammography that is rarely used today.
"We've come so far with improvements in breast imaging since that time, for example digital mammography, but even the (X-ray) film-screen mammography is totally different," Wadden, a radiologist who is medical director of the breast screening program for Newfoundland and Labrador, said from St. John's.
She estimates that up to 80 per cent of breast screening centres in Canada employ digital mammography, which allows radiologists to assess high-resolution breast images on a computer screen. As well, radiologists are now better trained "to recognize cancers at an earlier stage than when those trials were conducted," said Wadden.
"So the conclusion from those trials is not relevant to the way that breast imaging occurs in 2011."
Tonelli said the task force didn't pick and choose, but looked at all high-quality randomized control trials that compared screening and not screening, "and we don't find any evidence that more recent studies reached different conclusions about the benefits of mammography."
"There is no question that digital mammography is more sensitive, meaning that it picks up smaller abnormalities than film mammography," he said. "But there is no evidence that digital mammography improves outcomes to a greater extent than film mammography.
"In fact, there is reason to think that digital mammography may be associated with a higher risk of false-positives than the older technology."
This year in Canada, an estimated 23,600 women overall will be diagnosed with breast cancer and an estimated 5,100 will die of the disease. Among them will be about 390 women age 40 to 49, including those with a high risk of breast cancer due to family history or a genetic mutation. Some of their cancers may be caught by mammograms, others not.
But the Canadian Association of Radiologists contends more women will die of breast cancer if the guidelines -- which also stretch the interval between mammograms to two to three years for women 50 to 74 -- are followed.
"I certainly hope not, but I am concerned that women will not get their mammogram in a timely fashion," said Wadden, adding that so-called interval tumours can arise and grow unchecked between mammograms. "And we do know that the earlier you find a cancer, the better the prognosis. This is not unique to breast cancers, this is with all types of cancers."
"The numbers I have read from non-task force commentators have been purely speculation. In my opinion, they are overestimates of overestimates," said Tonelli.
"I think we need to be really careful that we don't start scaring women into a default choice. The whole purpose of our guidelines is to try to allow women to make an informed decision, and in my opinion introducing this element of fear is counterproductive."
In fact, research shows that worldwide, the rates of death from breast cancer have actually been declining -- even among populations without routine screening programs.
While mammography studies in the 1960s to the early '80s showed mammography translated into lower death rates, the subsequent use of the preventive drug tamoxifen and the addition of post-surgical chemotherapy for women diagnosed with breast cancer appears to have changed the picture, said epidemiologist Dr. Cornelia Baines of the University of Toronto.
In the '70s and '80s, screening mammography did reduce mortality, Baines agreed. "But in 2011, therapy is achieving so much, there's not much room for screening to have any impact."
And the programs are extremely costly, she said. In Canada, estimates are pegged as high as $500 million a year.
"It's too much money to spend, I think, for benefit achieved," said Baines, who has been studying the effectiveness of screening for more than 20 years. "But that's just my opinion."
Indeed, some opponents have accused the task force of putting taxpayer dollars ahead of women's health. But Tonelli said cost was never an issue. "Not one bit. All we considered were risks and benefits."
Radiologists' motives have also come under scrutiny, with some accusing the profession of conflict of interest and trying to protect a source of income from analyzing mammograms.
Wadden rejected that notion, saying that the money radiologists make from mammography "is actually very low. I could make more money doing other things, such as reading CT scans.
"So nobody's getting rich reading mammograms. We do this because we're passionate about it."
In the end, all the claims and counterclaims about the value of routine mammography may be a moot point.
Despite all the dos and don'ts in the guidelines, the overriding message is that women need to discuss the potential harms and benefits of routine screening with their doctors, then decide what's best for them as an individual.
And no once is saying a woman in her 40s, at average risk of developing breast cancer, can't get the test if she wants one, agreed Dr. Ruth Wilson, a family physician in Kingston, Ont.
"Some women are very definite they don't want to have a mammogram. They don't like them, they don't want them, they don't see the point," said Wilson, associate director of health policy for the College of Family Physicians of Canada, which endorses the guidelines.
"Other women are very health conscious and want to do absolutely everything they can to protect their health," she said, adding that doctors can order a screening mammogram if a woman wants one.
"It's not a block," she said of the recommendations. "They're guidelines, that's what they are. They're not rules about funding or limiting access or anything like that."