Study: Mammograms Produce High Level Of False Results

During a 10-year-period, one out of three women who had

mammograms and breast exams had abnormal results that

required additional testing even though no breast cancer was present, according to researchers at the University of Washington and Harvard Medical School.

The scientists' interest in performing the study came from

concerns and anxiety expressed by patients over abnormal screening results. Additional testing can be stressful, time-consuming, and costly. Earlier research had shown that, nationally, about 1 mammogram in 10 produces a false-positive.

The study determined that one woman in two will receive a false-positive result after having annual mammograms for a decade, and almost 20 percent of women will undergo a biopsy. The study also indicates that almost 25 percent of women will have a false-positive result at some point in 10 years of clinical breast exams.

The study was conducted at Harvard Pilgrim Health Care, a large health maintenance organization affiliated with Harvard Medical School, and published in today's issue of the New England Journal of Medicine.

"If a woman is screened for breast cancer every year between age 40 and age 70, she could have a total of 30 screening mammograms and 30 clinical breast exams," said Joann Elmore, assistant professor of medicine and epidemiology at the University of Washington and lead author of the study. "There's a high chance of a woman having an alarming false-positive episode."

"We hope that as women learn how common false-positives are over time, they will feel less anxious if they are told their mammogram is abnormal and they require additional tests," said Mary Barton in the Department of Ambulatory Care and Prevention, a jointly-run department of Harvard Medical School and Harvard Pilgrim Health Care.

Elmore, Barton, and their team looked at computerized records for 10 years of breast-cancer screening and diagnostic evaluations performed on 2,400 women aged 40 to 69 at entry into the study. A total of 9,762 mammograms were read by 93 radiologists, and 10,905 clinical breast exams were performed by 381 health care providers.

With a median of four mammograms per woman, 23.8 percent had at least one false-positive mammogram over the 10-year period. With a median of five clinical breast examinations per woman, 13.4 percent had at least one false-positive. A total of 31.7 percent had at least one false-positive result for either test.

The false positives led to 870 outpatient appointments, 539 diagnostic mammograms, 186 ultrasound examinations, 188 biopsies, and one hospitalization. For every $100 spent for screening, an additional $33 was spent to evaluate the false-positive results.

The investigators believe the study may, in fact, underestimate the false-positive rate for mammography in the United States. The overall rate of abnormal mammograms at Harvard Pilgrim Health Care was only 6.5 percent, whereas the national rate is nearly twice as high. In comparison, only 2 percent to 5 percent of mammograms are read as abnormal in Sweden.

The possibility that radiologists in the U.S. are interpreting too many mammograms as abnormal should be investigated, the researchers believe.

If their findings are representative, the researchers estimate that as many as 16 million women in the U.S. would have at least one false-positive mammogram and 7 million would have at least one false-positive clinical breast examination after 10 years of annual screening.

The researchers recommend that women be informed about the chances of a false-positive test result, and that healthcare providers be trained to deal with such results.