Mammograms: Pain for nothing? - The Age - Saturday, 16 February, 2002
For decades, it was an article of medical faith: get a mammogram; it could save your life. Now, seemingly overnight, that faith has been shaken. The mammogram - a yearly ritual for millions of women - has become - the focus of a scientific dispute that has spilled from the pages of medical journals into the columns of daily newspapers.
In the end, it is unlikely there will be a quick answer to the central question of whether researchers were right when they said that screening healthy women reduced death from breast cancer.
The mammogram has always 'been a modest weapon, with benefits that women must weigh against possible risks. It is a screening tool that misses some tumours. At most, studies have found, it can cut the breast cancer death rate by 30 per cent.
Even when mammograms work, what they find does not always turn out to be cancer. Or the cancer they find may be growing so slowly that it would never :threaten a woman's life. The result can be surgery, radiation and chemotherapy that are not medically necessary.
Over the years, public debate about the usefulness of mammograms has focused on which age groups should be routinely screened. If it is useful for women over 50, then why not extend it to women in their 40s or even 30s? Meanwhile, scientists and statisticians have quietly debated a much broader issue - do mammograms at any age have merit?
The larger issue came to light last year with the publication, in the British science journal The Lancet, of a study by two researchers based in Denmark. They argued that the clinical trials most often cited to support recommendations for mammograms were too flawed to be reliable.
Last month, an independent panel of experts within the United States National Cancer Institute agreed and said it could no longer make a recommendation about whether women should be screened. But then, after reviewing the matter, the cancer institute concluded that the new analysis did not refute evidence that mammography works.
The institute decided that, despite the panel's view, it would stand by the recommendation that women 40 and older be screened. (In Australia, the target group is women over 50.)
Many of those who did the original trials are defending their work They say that while there are flaws in the studies, the Danish analysis exaggerated their significance and misinterpreted fections," said Dr Steven Woolf, a member of the US Preventive Services Task Force, a panel that reviews scientific evidence about disease prevention. "But the issue is whether they invalidate the studies. My own view is that they do not rise to that level."
Since a new trial would require tens of thousands of women and a decade for results, some scientists are talking about digging deeper and more carefully into the old ones.
Mammography supporters, led by the American Cancer Society, worry that the uncertainty will weaken the US Government's resolve to back routine screening. They say mammography is a leading reason for the breast cancer death rate dropping in the past decade.Even when mammograms work, what they find does not always turn out to be cancer. Others, including those scepti cal of mammography, ask whether the decline is a result of better treatments, especially the drug tamoxifen. For them, the furore is an opportunity to turn the focus of the war against breast cancer towards better treatment and the search for a sore.
An estimated 30 million women in the US have annual mammograms, and many are having additional tests, like sonograms, when findings are suspicious. This costs more than $US3 billion ($A5.9 billion) a year, said Dr Martin Brown, an economist at the US National Cancer Institute.
From the start, there was concern among scientists that mammograms did not work as well for women in their 40s, whose denser breasts make tumours harder to spot and who are much less likely than older women to have breast cancer in the first place.
As a result, the US cancer institute flip-flopped four times between 1977 and 1997 on its recommendation on whether women in their 40s should or should not undergo routine screening. But if by then the guidance for women in their 40s was murky, the consensus that screening worked for older women would soon be thrown into doubt.
Dr Peter Gotzsche belonged to a research collective in Copenhagen, Denmark, known as the Cochrane Collaboration, which is striving to Prove the quality of scientific studies and reporting. When he and his colleague, Ole Olsen, looked at the seven large clinical trials on mammography, they concluded that they were too flawed to support mammography recommendations.
The report initially drew little public attention. It was their deeper analysis, published in The Lancet in October, that touched off a firestorm.
Gotzsche and Olsen cited a number of things they said weakened the research, such as potentially inaccurate records of causes of death, differences in screening schedules, and possible discrepancies in the health histories of women in one of the trials.
But while some leading medical experts were convinced, others maintained that the Danish critique misinterpreted data, failed to account for statistical adjustments that corrected problems, read too much into disparities in the numbers and raised alarming questions without offering evidence that the results were actually skewed.
Last month, the panel at the US National Cancer Institute concurred with the Danish report and said it would be as rational for a woman to decide not to have the test as to decide to have it.
But others, including scientists who have long looked sceptically at mammography, say they are not convinced that the mammography trials were so flawed that their results should be ignored.
For women and their doctors, the uncertainty is immensely exasperating, given that nearly four decades have passed since researchers began trying to find out if mammograms work.
Moreover, scientists say that the value of mammography cannot be weighed without taking into account the complex biology of breast cancer and the increasing effectiveness of treatment.
Some tumours grow so fast that mammograms cannot spot them before they spread - and even if they could, the treatment might not be good enough to make any difference. In other cases, the treatment is so effective that it does not matter if the tumour is found with a mammogram or somewhat later, when a lump can be felt, voiding the whole need for early detection.
For now, even as they acknowledge mammography's limitations, many doctors say it is the best tool they have.
"I can think of many women where a mammogram was helpful in picking up something before it had spread ..." said Dr Lynn Hartmann, a breast cancer specialist at the Mayo Clinic in Minnesota. "So I am not at the point of saying we should discard this tool."