Women in Canada can be screened less frequently for breast cancer and doctors should stop performing routine breast examinations altogether in women without symptoms of the disease, according to new Canadian breast cancer screening recommendations.
The guidelines for average-risk women – updated for the first time in a decade – recommend no routine mammography screening for women aged 40 to 49 and lengthen the screening window for women ages 50 to 74 from every other year, to every two to three years.
Women have been told for years that regular mammograms save lives.
But in what could become a flash point in the debate about the benefits of the breast X-rays, the authors state that the absolute benefits of screening women aged 50 to 69 “remain small” and that a substantial portion will have false positive results – leading to “unnecessary and invasive investigation,” they said. In some cases it can lead to women having part or all of their breasts removed when, in fact, they do not have cancer.
Story continues below
Women need to weigh the benefits and harms of mammography, the authors state, adding that women aged 50 to 69 “who do not place a high value on a small reduction in mortality and who are concerned about false-positive results, unnecessary diagnostic testing and potential over diagnosis of breast cancer are likely to decline screening.”
“We’re not trying to come across as saying that breast cancer screening with mammography is not useful,” said Dr. Marcello Tonelli, chair of The Canadian Task Force on Preventive Health Care and associate professor in the department of medicine at the University of Alberta in Edmonton.
“We think it is a potentially useful tool in the fight against cancer. But it’s important for women to be informed about the risks and benefits – to know that both are present, that it’s not all benefit and to realize, when they make that assessment, the magnitude of what they’re talking about.”
“If you look at the numbers, you are much more likely to have a false positive result than you are to have your life saved by screening,” Tonelli said. “It’s a real benefit, but compared with the risk of false positives, it’s relatively small.”
Appearing in this week’s issue of Canada’s top medical journal, the guidelines also recommend against doctors routinely performing breast examinations to screen for cancer – a change from the previous guidelines.
They also recommend against women checking their breasts monthly for signs of cancer, a hold over from the 2001 guidelines.
The authors state that no case can be made for screening all women for breast cancer beginning at age 40 – a controversial practice not followed in most of Canada but which had until recently been the recommendation in the U.S.
Only Prince Edward Island actively recruits women aged 40 to 49 for mammography screening. Overwhelmingly the provinces require a doctor’s referral for younger women.
In the 50 to 69 age group, the standard is screening every two years.
The new guidelines, published in this week’s issue of the Canadian Medical Association Journal, challenge the view that women who choose not to be screened are somehow “irresponsible,” according to a related commentary.
Dr. Peter Gotzsche, director of the Nordic Cochrane Centre in Copenhagen, Denmark says that any possible effect of screening on breast cancer deaths is “marginal” and that women have not been informed of the potential harms.
“There is massive over diagnosis,” he said in an interview with Postmedia News. “It is a disaster to be healthy one day and the next day become a breast-cancer patient.”
The tests can detect tumours that never would have threatened a woman’s life, he said, exposing women to unnecessary treatment that in itself can be life-shortening, as well as unnecessary lumpectomies or mastectomies.
Many women harbour harmless cell changes or cancers in their breast, Gotzsche said.
“If (mammography) had been a drug it would have been removed from the market immediately,” he said. “You cannot have a drug that harms the healthy population on such a grand scale and with a doubtful effect.”
The guidelines are intended for average-risk women – meaning women who do not have a previous history of the disease, who do not have a known genetic mutation or other risk factors for breast cancer.
According to the new guidelines, the absolute benefit of screening is lower among women aged 40 to 49, because of their lower risk of breast cancer to begin with. Screening about 2,100 women aged 40 to 49 once every two to three years for about 11 years would prevent a single death from breast cancer, the task force says. But about 690 women would have a false positive result, leading to unnecessary followup testing; 75 women would have an unnecessary biopsy of their breast.
For women aged 50 to 69, screening about 720 women once every two to three years for about 11 years would prevent one death from breast cancer, but it would also result in about 204 women having a false-positive result and 26 women undergoing a breast biopsy.
Tonelli said screening older women every three years “seems to preserve the benefits associated with screening more frequently” but might reduce the harms. He said the costs of testing did not influence the group’s recommendations.
Mammography can detect tumours when they’re smaller and more responsive to treatment, Tonelli said.
But some tumours are so aggressive that it makes no difference when they’ve been detected, he said. Others are so slow-growing they would not affect a woman’s health or life-expectancy.
No evidence was found to show that routine breast examinations by doctors in women who have no symptoms of disease prevent deaths from breast cancer. If anything, it can lead to unnecessary biopsies and procedures.
“When doctors examine the breasts of women who have no complaints, sometimes they find a mass – and more often than not those masses are benign,” Tonelli said.
His group also says doctors shouldn’t be teaching the kind of structured breast self-examination long taught to women. Large randomized trials show that it doesn’t reduce mortality from breast cancer and significantly increases the number of unnecessary interventions.
“If you go regularly looking (for breast cancer), most of those lumps and masses that are found are not cancer,” Tonelli said.
“We’re not saying that if a woman notices something with her breast that it should be ignored,” he stressed. A mass, lump, discharge or any change is reason to see a doctor.
Tonelli said individual women should discuss the risks and benefits of mammography screening with their doctors.
The College of Family Physicians of Canada has endorsed the guidelines.
Here are the key recommendations for breast cancer screening from the Canadian Task Force on Preventive Health Care:
– No routine mammography for women aged 40 to 49. The absolute benefit is lower for this age group than for older women because of their lower risk of cancer.
– For women aged 50 to 74, routine screening with mammography every two to three years.
– No screening of average-risk women using MRI.
– No routine clinical breast exams or breast self-exams to screen for breast cancer.