Study Warns of Mammogram False Alarms
A woman who has regular mammograms and clinical breast exams will almost certainly have at least one false alarm during her lifetime that will require stressful, time-consuming and expensive further testing to rule out breast cancer, according to a new study reported today.
One in five of those false alarms will lead to a breast biopsy in which tissue is removed from the suspected tumor, a team from the University of Washington School of Medicine and Harvard Medical School reports in today’s New England Journal of Medicine.
According to the study, 50% of women who have 10 mammograms will have one so-called false positive result. The high rate is an outgrowth of physicians’ efforts to detect every breast tumor possible, said Dr. Joann G. Elmore of the University of Washington.
Although increased efforts should be directed at reducing the number of false positives, she said, the study carries a hopeful message.
When women receive a positive result on a mammogram or clinical examination, “it is very scary,” Elmore said. “Many feel all alone. If they realize that [false positives] are common, they may be better able to go through the diagnostic process with less anxiety.”
“Women need to know that just because there is an abnormality in their mammogram, it doesn’t necessarily mean they have cancer,” added Dr. Lawrence Bassett, director of the Iris Cantor Center for Breast Imaging at the UCLA-Jonsson Comprehensive Cancer Center.
But the finding is unlikely to change recommendations by the American Cancer Society and the National Cancer Institute that women have a mammogram every other year in their 40s and every year after they reach 50.
Mammography is a very effective way of detecting breast cancers, noted Dr. Harold C. Sox of Dartmouth-Hitchcock Medical Center in Lebanon, N.H. Yearly screening for women between 50 and 79, he noted in an editorial in the same issue of the journal, reduces the risk of dying from breast cancer by 26%.
Abnormal Findings
Elmore and her colleagues studied 2,400 female members of Harvard Pilgrim Health Care, a health maintenance organization in Boston. All were between 40 and 69 when they entered the study and had no signs of breast cancer. A total of 9,762 screening mammograms were read by 93 radiologists, and 10,905 screening clinical breast exams were performed by 381 physicians and nurses. An exam was declared a false positive if an abnormal result was not followed by a diagnosis of breast cancer within the following year.
In addition to the 50% false-positive rate among women who had 10 mammograms, the researchers also found a 25% rate among those who had 10 clinical breast examinations. The false positives in the study led to 870 outpatient appointments, 539 diagnostic mammograms, 186 ultrasound examinations, 188 biopsies and one hospitalization (for an infection that followed a biopsy).
False positives were most common among women in their 40s, and the incidence declined in each subsequent decade of life, the study found.
The abnormal findings on the mammograms were often caused by cysts, or occurred with young women with very dense breasts and older women undergoing hormone replacement therapy that caused changes in their breasts.
The team concluded that for every $100 spent on screening, an additional $33 was spent to evaluate false positives.
“This is a well-done study that provides a useful piece of information,” said Dr. Barnett Kramer, deputy director of the National Cancer Institute’s division of cancer prevention. “Women need to be aware of both the positive potentials of mammography and the downsides, because there are some, just like there are with any other medical technology.”
A Constant Balancing Act
Because the study followed the women for only 10 years, it did not formally address the lifetime chances of being diagnosed with at least one false positive. But most women have 25 to 30 mammograms between the ages of 40 and 70, and if the odds of a false positive are 1 in 2 for 10 mammograms, then the chances approach certainty for such a large number.
“Sooner or later, if a woman has an annual mammogram, she is likely going to have a false positive,” Elmore said. “Many will experience more than one.”
The study may even have underestimated the risk of a false positive. At Harvard Pilgrim, about 6.5% of the screening mammograms showed an abnormality. Nationally, about 10% of mammograms shows an abnormality, suggesting a correspondingly higher rate of false positives.
Some false positives cannot be avoided, UCLA’s Bassett said. “We’re constantly in a balancing act. In order to find the smallest cancers, we have to have some false positives,” he said.
But the rate can probably be reduced, most experts agreed. In Sweden, for example, the incidence of false positives is between 2% and 5%, and there is no evidence that more tumors go undetected there, Kramer noted. “It seems like it [reducing false positives] should be doable,” he said.
Anxiety produced by false positives can often be alleviated by the growing trend of having a radiologist read the mammogram while the patient is still in the office. “If we see something we are concerned about, just one more picture is often enough to resolve the concerns,” Bassett said.
Dr. Mary B. Martin of Harvard Pilgrim noted that the HMO is experimenting with having a radiologist read the mammogram even before a woman puts her clothes back on, so that another scan can be taken if necessary.
Women--especially those in their 40s--who are trying to decide whether or not to undergo yearly mammograms can get more information about potential risks and benefits at https://mammography.ucsf.edu/inform/index.cfm
