The purpose of mammography is to stop breast cancer before it can spread. But two recent reports–one on false positives, the other on false negatives–are reminding those of us in the trade that neither the tests nor those who analyze them are perfect.
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All mammograms are read by radiologists, but not all radiologists read mammograms, at least not equally well. And not all mammograms are equally readable.
Even among people, like me, who do specialize, there is variability.
At the risk of sounding defensive, I should point out that mammograms are devilishly hard to decipher and routine screening for breast cancer has been promoted actively for about only 10 years. The strengths and limitations of the technique are not yet well understood–not by patients or their doctors; not by clinics that do the procedure or insurers who pay for it; not even by the regulatory agencies themselves.
Perhaps some insights from this side of the X-ray may help women make informed choices.
Early breast cancers are subtle. They may hide behind other tissues or appear on the film as tiny white specks–like salt on a cotton ball or a white rabbit in a snowstorm. That’s why radiologists preach yearly exams.
Most breast tumors grow slowly, and nothing very dramatic is likely to happen in a year. But those of us who hunt them in hopes of spotting them before they do become obvious want a couple chances. The more shots we have at the X-rays of an individual, the better the odds of our finally seeing something we might have missed before.
That is the real reason for urging annual mammograms for certain women and why it is crucial that they bring in their previous X-rays, if they are not already on file: We look for changes over time.
Of course, the harder we look sometimes, the more suspicious things we may find. Or perhaps experience warns us that certain patterns, shadows or dots merit further investigation. From this arises the problem of the false positive, which, of course, is much more annoying to the patient than to the physician.
A week after your mammogram, as you wait a little nervously for that letter saying everything is OK, they call you instead and request that you come back in for “magnification views of a suspicious area.”
You make an appointment as soon as possible, mull over the family medical history, check your insurance, grit your teeth and go through it again. When you get those follow-up X-rays, your doctor takes a close look, then perhaps announces: “Nothing to worry about. We just like to be sure. See you next year.”
According to a recent widely publicized study in the New England Journal of Medicine, women stand a 25 percent chance of this frightening experience happening at least once over a decade of mammograms. From my standpoint, despite the anxiety it causes any patient, a false positive result is not the worst thing in the world. The worry often stops after another X-ray.
In the New England Journal study, only one half of 1 percent of patients who were called back required a biopsy before being cleared as normal. (Ordinarily, there are only about five cancers found per 1,000 screening mammograms.)
My interest as a researcher is in false negatives–cancers that might have been detected from a mammogram but were missed. I collect such damning X-rays from everywhere and present them as teaching tools at conferences for fellow radiologists and to refine the skills of a computer system being developed at my institution as a way perhaps to provide us with automated second opinions.
Two weeks ago at the American College of Radiology’s 28th National Conference on Breast Cancer, in Washington, D.C., I presented the results of a study we had conducted in efforts to find out how much variability exists among the specialists.
The test was rather simple: The radiologists described their mammogram-reading skills–rating themselves, as it were–and then looked at 100 collected films and tried to find the cancers.
It turned out that even those who consider themselves experts at reading mammograms were able to find four cancers out of every five that were there–and this was in a test setting where they knew there were likely to be plenty of tumors present.
As one might expect, the experts scored better (by 16 percent) than the general radiologists–those who spend their days reading everything from chest X-rays to CT scans. They found 70 percent of the breast cancers, on average.
l don’t have the statistics to break down our field into mammography specialists and generalists–other than to say that there are far more of them than of us–but I could argue that if screening were organized on a large scale and all the exams were read by experts, we would find many more breast cancers and probably decrease the number of false-positive call-backs for patients who are normal.
But most mammograms in this country are being read by generalists.
The enormous variation that I and other studies may have tapped into means that mammography is not being given the best chance to do its job. We humans simply are not yet as good as the machines.
How should a woman deal with this?
First, get vocal. Demand good mammograms read by someone who really knows how. That means going to a facility that specializes in it and where volume is high, such as a university or a large breast-diagnostic center.
Second (and this is important enough for me to repeat it) bring along your previous mammogram–better yet, all your previous mammograms–because mammography works best when doctors can look for changes.
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Unfortunately, it is almost impossible these days to do this.
Hospitals promote fire sales on mammograms to lure in new patients without any regard for the process or the need for prior studies. Managed-care organizations trade or sell “managed lives” and devise new contracts that may send patients to different facilities each year.
Copied films that we receive are often inferior and sometimes useless. Federal law (Mammography Quality Standards Act, to take full effect in 1999) might put a stop to this practice but not soon enough to avoid mammography having acquired a “too-much-fuss” reputation among too many women.
Third, don’t waste a lot of energy worrying about false positives. Yes, there are many more false alarms than true cancers even in the best of hands, but these can usually be dealt with in a straightforward fashion. And it doesn’t pay to panic: More than 30 percent of women referred to our institution for biopsy turn out not to need one, for example. And when it becomes crucial that cells be collected for analysis, it most often can be done by needle rather than open surgery.
Fourth, if I were a woman over 40 and at risk of breast cancer, I would program myself to go each year like clockwork for the unique test for early cancer that could save my life. I would realize that normal means normal, that most mammograms are clear, and I would try to talk myself out of undue worry. I would pick a convenient time, when the tulips bloom or the kids go back to school, for instance, but not the week before my two-week vacation.
And I would give my radiologists multiple chances to get perfect.