New Study Defends Mammograms; Doctors Lament Conflicting Signals
Mammography continues to be an effective way to reduce deaths from breast cancer, according to a new analysis of long-term data, and women should continue to undergo regular screening, several national medical organizations said Thursday.
For women aged 55 and older who were followed for eight to 11 years, routinely being screened for tumors reduced the risk of death from breast cancer by 55%, according to the new analysis reported in this week’s edition of the international medical journal the Lancet. For women who were aged 45 to 54 at the beginning of the study, screening led to a 30% reduction in deaths, the researchers said.
The new study is the latest--although almost certainly not the last--word in a confusing debate over the benefits of routine breast X-rays. Particularly in recent months, the debate has sent conflicting signals to women over whether they can reduce their risk of dying from breast cancer by routinely having mammograms.
The long-running debate heated up in October after another study that was also published in the Lancet. That study, conducted by two researchers in Denmark, concluded that existing evidence did not prove that mammograms actually do any good. Since then, a widely consulted medical reference service for doctors has issued a statement echoing the conclusions of the Danish study.
The controversy has troubled many cancer doctors. “We are deeply concerned that the current discussion might deter women from screening” for breast cancer, said Dr. Larry Norton, the president of the American Society for Clinical Oncology.
In an effort to resolve the issues over mammograms, the society said Thursday that it would call together all interested parties within the next two weeks to evaluate all the evidence about mammography and develop up-to-date guidelines.
Until new guidelines can be developed--probably by May--women should continue to follow the current advice that all women over the age of 40 have an annual mammogram, Norton said. An estimated 50 million women receive mammograms each year.
In a joint statement, the American Cancer Society, the American Medical Assn. and eight other health groups made the same recommendation Thursday. “If women are dissuaded from getting regular mammograms, lives will be lost,” according to the statement, which the groups placed as a full-page advertisement in the New York Times.
Last October’s study was conducted by Dr. Ole Olson and Dr. Peter Gotzche of the Nordic Cochrane Centre in Copenhagen. They analyzed seven large trials of mammography and concluded that five of them, which had supported mammograms, were so flawed that their results were meaningless.
The remaining two studies, one performed in Malmo, Sweden, and one in Canada, failed to prove that screening was effective in reducing death rates, Olson and Gotzche said.
The new study, conducted by a team led by Dr. Claudia Henschke of the Cornell Medical Center in New York City, rebutted the work of Olson and Gotzche. The Danish researchers simply did not monitor patients long enough, Henschke and her colleagues reported.
“Screening does not have an immediate effect,” Henschke said. “The deaths that get to be prevented by screening are in the future, years away. . . . Therefore, the screening itself must continue for a sufficiently long time to realize its benefit.”
Henschke’s team looked at data from the Malmo study, which followed women for more than six years. The previous analysis by Olson and Gotzche had not looked at data from such a lengthy period.
“The issue here is that deaths that occur very early in the follow-up period are deaths that screening has very little opportunity to help avoid,” said Dr. Robert Smith of the ACS.
In other words, when a screening program is first started, many of the tumors initially detected will have been found too late to cure. As a result, in the first years of a screening program, little difference will be found between the death rates of women who have been screened and those who have not been. Screening helps women whose tumors are found early and would not have caused death for many years so the benefits become apparent only after considerable time.
“This, and the weight of so much other evidence, confirms that mammography is . . . a very good tool we have right now--the most important tool that can measurably contribute to reducing deaths from breast cancer,” Smith said.
Another complicating factor in the debate is that all of the clinical trials under discussion are at least 10 years old--some are twice that age. Since then, “mammography has improved, and there are better methods of biopsy for small lesions,” said Dr. Peter Greenwald of the National Cancer Institute. “Hormonal therapy, chemotherapy, surgery and radiation have all improved. All of these could improve the outcome of mammographic screening.”
But Dr. Donald A. Berry of the M.D. Anderson Cancer Center said he finds the new paper unimpressive. “They wanted to find a positive result, and the only positive result was Malmo,” he said. “The question is, ‘Is the paper compelling?’ No, it’s not.”
Berry is in charge of drawing up new guidelines about mammography for Physician Data Query, an online database sponsored by the National Cancer Institute. Its recommendations are formed by an independent board and are not necessarily the same as those of the cancer institute itself.
At a recent meeting, the board of the data query concluded that there are not enough data available to determine whether mammography is effective or not.
“It’s conceivable that mammography is beneficial,” Berry said. “It’s conceivable that it is not. If it is, the benefit is not spectacular. And while we don’t understand if there is a benefit, we do understand that there is a risk.”
The main risk comes from the fact that only 2% to 11% of all “abnormalities” detected by mammograms actually turn out to be cancer. That means a lot of women undergo unnecessary subsequent mammograms, as well as needle aspirations, biopsies and other invasive procedures.
“We think women should be told about both the benefits and the risks and allowed to choose for themselves,” Berry said.
