Merits of Mammography Being Debated -- Again
Oct. 18, 2001 -- The nation's leading healthcare agencies -- including the American Cancer Society and the National Cancer Institute -- strongly advise mammography for women as the best defense against breast cancer, based on scientific evidence that it provides early detection of treatable tumors.
But a group of Danish researchers has published a controversial study claiming that virtually all studies of mammography are seriously flawed and that they fail to show that the screenings prevent death.
"The majority of the trials are of poor quality, so you cannot make any strong conclusions about mammography's effectiveness," says lead author Ole Olsen, senior researcher at Nordic Cochrane Center in Copenhagen, Denmark. "Two of the best trials do not indicate any reduction in mortality."
This is the second such report the group has published in The Lancet. Last year, their analysis of the eight clinical trials -- involving half-a-million women -- drew sharp criticism from cancer experts.
The American Cancer Society has been vehement in its denial of Olsen's claims.
The Danish reports are "profoundly irresponsible ... a disservice to women," says Robert Smith, PhD, director of cancer screening for the American Cancer Society. "Last year, their report was soundly thrashed in the scientific literature as an incompetent treatment of a very important issue. The Lancet received over 1,000 letters from the world's cancer experts, all overwhelmingly negative."
In researching his current report, Olsen says he retrieved more than 200 reports and has much more information about how trials were carried out. "What we found confirmed and strengthened our original conclusions," he tells WebMD.
He found inadequacies in data, including missing and incomplete data, he says.
Altogether, the studies create "statistical uncertainty," Olsen says. "We're not saying there is absolutely no effect [of mammography] whatsoever. But the effectiveness is certainly not as high as has been believed."
When there is a reduction [in deaths from breast cancer], if anything, it's a small reduction," he tells WebMD.
"There may even be harm," he says. "Women who have mammography receive more radiation therapy and seem to be receiving more surgery." Regular screening identifies some slow-growing benign tumors that would never have developed into cancer in the women's remaining lifetimes, as well as cell changes that are benign, he says.
Olsen's allegations "are not grounded in scientific literature," says Smith. "Evidence shows that, if anything, we are treating women less aggressively for breast cancer as a result of finding smaller tumors."
"What he's calling 'flaws,' some of the issues he's raising, are completely inappropriate for trials of a preventive health service," Smith tells WebMD. "He is analyzing these studies as if he's evaluating a treatment -- whether they're dying from the disease or if the treatment is causing them to die for some other reason."