Six prominent Cornell University doctors say they have important new evidence showing that mammography can save lives.
Their analysis, appearing in the journal The Lancet, comes on the heels of a highly publicised report issued earlier this month by an advisory panel of the National Cancer Institute that concluded that screening mammography has little or no life-saving value.
Previous study’s findings flawed
The Cornell team based its findings on the same data examined by the advisory panel - an analysis of seven breast-cancer studies published last year in The Lancet by European researchers Drs Ole Olsen and Peter Gotzsche. The Cornell team said the two researchers' findings were seriously flawed.
"The biggest mistake is that the analysis simply did not look far enough into the future of the women to get a true picture of the value of mammography," says Dr Claudia Henschke, lead author of the new Lancet review, and professor of radiology at New York Weill Cornell Medical College.
Often, the life-saving value of screening mammography does not become apparent until at least eight years after a cancer has been discovered, cancer experts say. (There are two types of mammography - screening and diagnostic. A screening mammogram is done on a regular basis when no symptoms of disease are present. A diagnostic mammogram is performed after a woman or her doctor has discovered a lump or other abnormality that needs further analysis.)
Study used limited data
Olsen's and Gotzsche's research also has been widely criticised because, while they originally analysed seven studies, they gleaned their findings primarily from just two.
In one, a Canadian trial, the women were only followed for four years after their cancers were diagnosed - not nearly long enough to see any life-saving results from screening mammography, says Henschke.
The second study - known as the Malmo trial - included an 11-year follow-up. But, Henschke says, the calculations made by Olsen and Gotzsche also were premature.
For instance, she says, when Olsen and Gotzsche analysed a five-year follow-up of women 55 or older, they noted 16 deaths among breast-cancer patients who had regular screening mammography. This compared to just 13 deaths in the group that had no screening mammography. Overall, the study showed 63 breast-cancer deaths in the screened population, and 66 in the unscreened group.
But once the Cornell doctors re-examined the numbers, and looked at the data year by year, they came up with an entirely different statistical picture. They also were able to put their finger on one of the major flaws in the original analysis, they say.
"When we analysed the same study [the Malmo trial] looking from year eight through year 11, the death rate changed dramatically, with just 14 of the women who underwent screening mammography dying, compared to 31 deaths among the women who did not have the screening mammography," says Henschke.
New study more sound
The current controversy centres on whether there is value in screening mammography, and if those women who are screened regularly live longer if a cancer is discovered.
Breast cancer expert Dr David Dershaw says the Cornell re-analysis is sound science.
"Once you get out to about seven years, in all the studies, the data is pretty compelling in favour of mammography," says Dershaw, director of the Breast Imaging Centre at Memorial Sloan Kettering Cancer Centre.
In some studies, he adds, favourable results can be seen as early as year three, "depending on the compounding factors, such as the quality of the mammogram, and the number of breast cancers in the study population."
Reasons for previous study’s flaws
So why didn't Olsen and Gotzsche - and the National Cancer Institute's advisory panel - find these same results? Dershaw believes they simply didn't look in the right places.
"In addition to not looking far enough into the future, they also relied too heavily on old data, and didn't bother to see how study results were re-analysed and updated" by the original researchers, he says.
In other instances, Dershaw contends, they simply chose to ignore data in support of mammography and concentrated on negative findings.
For example, he says, "They paid no attention to the fact that in countries that have already instituted nationwide mammography screening, the rate of death from breast cancer has dropped dramatically."
Study viewed as flawed from the start
Dershaw also notes that when Olsen's and Gotzsche's most recent findings were published, in October 2001, they were almost universally ignored, viewed by the medical profession as flawed right from the start.
"They only made a splash when they ended up on the front page of The New York Times - two months later," says Dershaw. Many believe the National Cancer Institute's advisory panel pursued its report only after that story appeared, he says.
While the NCI report has left many women wondering if screening mammography will do them any good, experts like Dershaw, Henschke and her Cornell colleagues insist it can save lives.
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