TORONTO – Most women age 40 to 49 should not have routine mammograms and those 50 to 69 can wait slightly longer between the tests than previously recommended, updated Canadian breast cancer screening guidelines advise.
And for the first time, the Canadian Task Force on Preventive Health Care that developed the guidelines says that women aged 70 to 74 should be getting mammograms on the same schedule as those 50 to 69.
The revamped guidelines, published Monday in the Canadian Medical Association Journal, apply to women with an average risk of developing the disease. They include those with no previous breast cancer, no history of the disease in a first-degree relative like a mother or sister, no known BRCA genetic mutation and no previous exposure to radiation of the chest wall.
In its previous set of guidelines penned in 2001, the expert panel made no recommendations for average-risk women in their 40s as to whether they should have routine screening or not.
But the task force now advises against the practice for that age group, saying the potential harms from false positives and unnecessary subsequent cancer treatment outweigh the possible benefit – a slight reduction in the number of deaths from the disease.
Story continues below
“Before there was no recommendation for or against, and clinical practice followed that lead,” said task force chair Dr. Marcello Tonelli of the University of Alberta. “Most organized screening programs don’t recruit women aged 40 to 49 years as a result.
“The biggest change of all is probably in the way in which we frame all of our recommendations, that breast cancer screening has risks and it has benefits, and how women weigh those up will influence their personal decision to be screened or not.”
In the 2001 guidelines, women 50 to 69 with an average risk of breast cancer were advised to have mammography every two years. But the new guide extends that period, saying such tests can be done every two to three years.
The panel now suggests women age 70 to 74 should also have mammograms every two to three years.
“In routine practice, one of the challenges in producing guidance and then implementing it in real life is that patients don’t turn up for screening or any other service on the anniversary of their last test,” said Tonelli.
“So the intent here was to give a range so that someone who is appearing for screening at two years and a day is still falling within recommended practice (and) even after two years and six months,” he said from Edmonton.
“We also wanted to signal that since the last set of guidelines were produced, there has been some evidence produced that longer screening intervals, like every three years, might be just as good as every year.”
The new guidelines have grown out of an intensive review of international clinical trials, which looked at the risk of developing breast cancer in the various age groups and the potential harms inherent in the breast X-ray that can arise from misdiagnosis.
“Specifically, the harms could range from a woman being told she has an abnormality on a mammogram and being asked to repeat the mammogram, being asked to go for a biopsy of her breast, being asked to have part or all of her breast removed, and all the way up to surgery and radiation and chemotherapy.
“These are the spectrum of possible harms, so if you don’t have breast cancer, but you have your breast removed and have surgery, I think we’d all agree that’s a harm of screening.”
The task force determined that screening 2,100 women every two to three years for about 11 years would prevent just one death from breast cancer. However, it also would result in 690 women having false-positives that would lead to unnecessary followup testing, including 75 women having unnecessary breast biopsies.
“For every woman that had cancer found with mammography, there are many more that have had a false positive result or a scare,” Tonelli said.
While no primary studies looked at the risk of overdiagnosis specifically among women 40 to 49 years, “data from our systematic review show that for every 1,000 women aged 39 years and older who are screened using mammography, five will have an unnecessary lumpectomy or mastectomy,” the authors write.
“In addition to unnecessary intervention, false-positive results can lead to fear, anxiety and distress.”
Dr. Cornelia Baines, an epidemiologist at the University of Toronto and one of the world’s foremost experts on breast cancer screening, lauded the task force’s recommendations, calling them “completely warranted.”
“All in all, I think it’s a superb set of guidelines that really are very, very carefully drawn, carefully thought out and totally justified on the basis of existing evidence.”
Still, she predicted they will be greeted with the same indignation and criticism that occurred in 2009 when the U.S. Preventive Services Task Force presented similar recommendations, which also advised women to defer routine mammograms until age 50.
The switch from the previous recommendation that American women in their 40s have a mammogram every year or two like their older sisters caused a firestorm of controversy.
If Baines has any criticism about the revamped Canadian guidelines, it is that they could have been clearer in illustrating the potential harms arising from false-positive results, which could “serve as a disincentive to wanting screening.”
“They don’t say it in a way that really hits home,” she said, noting that for women age 40 to 49, there is a one in three chance of having a false-positive result, and one in every 200 will be falsely diagnosed with breast cancer and unnecessarily treated.
“I had breast cancer,” said Baines. “I can’t imagine how I would feel if I thought there was a major chance that all the emotional upheaval, all the miseries of treatment, all the misery of followup, all the misery of diagnostic labelling was all useless because I didn’t really have breast cancer.
“I do know for a fact that only a minority of women who get breast cancer die of it.”
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.
The College of Family Physicians of Canada has endorsed the new guidelines, as has the Canadian Cancer Society.
Gillian Bromfield, director of cancer control policy for the Canadian Cancer Society, said they reinforce the organization’s own breast-screening recommendations, which suggest women 50 to 69 should have a mammogram every two years.
“For women age 50 to 69, all the major health organizations are quite consistent that this is the age group that should be getting screened on a regular basis,” she said. “When you get outside of that age range, that’s where you start to see a bit more inconsistency.”
Among women in their 40s, for example, the evidence isn’t particularly strong that routine mammograms help to save lives, Bromfield said. Even so, some women will still want screening and should talk to their doctors about the benefits and risks.
Indeed, that is the overriding advice of the guidelines, Tonelli stressed.
“They say: ‘Here is what you can expect to get in the way of benefits from screening and here’s what you might expect in the way of harms. And based on what you, yourself, feel about your trade-off of those risks and those benefits, you together with your doctor can make a decision that’s right for you.’”
In a related commentary, Dr. Peter Gotzsche of the Nordic Cochrane Centre in Copenhagen, calls the new guidelines “more balanced and more in accordance with the evidence than any previous recommendations.”
Gotzsche writes that scientific evidence does not support mammography screening and he argues that it could even be harmful because it can lead to unnecessary mastectomies.
“The main effect of screening is to produce patients with breast cancer from among healthy women who would have remained free of breast disease for the rest of their lives had they not undergone screening.”
Canadian Cancer Society: 杭州桑拿按摩论坛杭州夜生活cancer.ca
Note to readers: This is a corrected story. A previous version had an incorrect spelling for Bromfield