Annual mammograms don't cut rate of breast cancer deaths: Canadian study
Published Tuesday, February 11, 2014 6:30PM EST
Last Updated Tuesday, February 11, 2014 9:07PM EST
Annual mammograms don’t appear to reduce breast cancer death rates in middle-aged women compared to simple regular physical exams, concludes a huge new Canadian study that brings into questions whether such screenings are helpful.
The study, which tracked close to 90,000 women, found that annual mammograms often do more harm than good because they pick up a lot of small, harmless cancers that will never cause symptoms or death in a patient's lifetime.
In fact, the study found many of the breast cancers picked up by mammograms were “over-diagnosed,” meaning they were the small, harmless cancer forms.
Study author Dr. Cornelia J. Baines, of the Dalla Lana Faculty of Public Health at the University of Toronto, says it’s beginning to appear that mammograms are not reducing death rates.
“The whole underlying rationale for screening is to reduce deaths due to breast cancer. But if screening does not reduce deaths from breast cancer, what is the point of screening?” she wondered to CTV News.
“There is none. There’s no justification for spending in North America billions of dollars on breast screening.”
Regular mammographies have long been touted as the best way to catch breast cancer in its earliest stages and reduce deaths from the disease. But just as a number of studies has questioned the value of prostate screening tests, recent research has also questioned the value of mammograms.
This latest study began in 1980, when Toronto researchers began tracking 89,000 women between the ages of 40 and 59. Some of the women were randomly chosen to undergo five mammograms once a year over five years, while the rest were not screened at all.
Over the next 25 years, researchers tracked how many of the women were diagnosed with breast cancer as well as how many died of the disease. They found there was not much difference between the groups.
A total of 3,250 women who had regular mammograms were diagnosed with breast cancer, compared with 3,133 among the group that wasn’t screened (and who instead detected the cancers through physical exams).
As well, 500 women died of breast cancer in the mammogram group -- not far off from the 505 who died in the second group.
The full results have been published on bmj.com.
The study also found that at the end of the five-year screening period, 142 “over-diagnosed” breast cancers were found of in the mammography group compared to the other group.
The researchers say that the true rate of over-diagnosis might be even higher, because the study did not look at how many cases of a very early form of breast cancer called DCIS (ductal carcinoma in situ) were spotted. That form of breast cancer, sometimes called Stage 0 cancer, accounts for one in four breast cancers detected in most screening programs, the researchers point out.
Baines says this study paints a picture of the harms of mammograms.
“In addition to not changing the number of women who died from breast cancer, 22 per cent of the women who had an invasive breast cancer detected by screening actually would never have been bothered by their breast cancer. They were over-diagnosed and received unnecessary treatment,” she told CTV News.
The study authors conclude that their results support the view that the rationale for screening by mammography “should be urgently reassessed by policy-makers."
But others are not so sure.
Breast cancer patient Teresa Reid believes that a mammogram saved her life. The 54-year-old says a mammogram found three fast-growing tumours that had developed over the two years between her screenings.
“I do believe I am alive today because of the mammograms at Princess Margaret hospital,” she says. “…If I hadn’t had that mammogram, that cancer would have grown.”
Dr. Martin Yaffe, a professor in the department of Medical Imaging at the University of Toronto and a senior scientist in the Imaging Research Program at Sunnybrook Research Institute, says it’s not fair to compare the results of mammograms from 1980 to the much more sophisticated scans of today.
“The study, as it was done, used technology which is no longer current -- absolutely obsolete by today’s standards … So it is not surprising that the investigators didn’t find the effect that they were looking for,” he says.
Yaffe says more recent studies using current technology have shown a substantial reduction in breast cancer deaths with mammogram screening. What’s more, he says the newer technology is reducing the number of “false positives.”
The problem with this study, Yaffe adds, is that women are once again being given a mixed message.
“It is very confusing. I don’t blame them for being confused,” he says. “I think we owe it to women to use the best science to give them the best advice we have. And that advice is there is a benefit. Not every woman will decide to be screened, but certainly it is one way to reduce the risk of dying from breast cancer.”
With a report from CTV medical specialist Avis Favaro and producer Elizabeth St. Philip