UW News

April 15, 1998

Breast cancer screening exams produce high level of false-positive results

Researchers at the University of Washington and Harvard University have determined that at least one woman in two will receive a false-positive result after having annual screening mammograms for a decade, and almost 20 percent of women will undergo a biopsy.

Their study also indicates that almost 25 percent of women will have a false-positive result at some point in 10 years of clinical (physical) breast examinations.

Results of the study, led by Dr. Joann G. Elmore of the University of Washington School of Medicine, are published in the April 16 issue of the New England Journal of Medicine. The study was conducted at Harvard Pilgrim Health Care, a large health maintenance organization affiliated with Harvard Medical School.

A woman with a positive result must go through additional workup before she can be sure that the breast abnormality is not cancer. Such workups can include mammograms, ultrasounds, outpatient visits and biopsies. When she does not have cancer, it is called a false-positive.

Elmore’s interest in performing the study stemmed from the concerns and anxiety expressed by her patients over abnormal screening results. Earlier research has shown that, nationally, about one mammogram in 10 produces a false-positive.

“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,” she said. “There’s a high chance of a woman having an alarming false-positive episode.”

Elmore and her 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 screening mammograms were read by 93 radiologists, and 10,905 screening 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,” said Elmore.

The investigators believe the study may, in fact, underestimate the false-positive rate for mammography in the United States: the overall rate of abnormal screening 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 screening mammograms are read as abnormal in Sweden.

“The possibility that radiologists in the United States are interpreting too many mammograms as abnormal should be investigated,” they state.

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

“This study indicates that we need to develop ways to reduce the false-positive results of breast-cancer screening and their associated psychologic and economic costs,” said Elmore. “We hope this study will allow women to better understand their risk of a false-positive screening test, helping to reduce their anxiety when an abnormality is noted.”

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.

Elmore is an assistant professor of medicine and epidemiology at the University of Washington’s School of Medicine and School of Public Health and Community Medicine. Co-investigators are Dr. Mary Barton and Dr. Suzanne Fletcher of the Department of Ambulatory Care and Prevention, a jointly-run department of Harvard Medical School and Harvard Pilgrim Health Care; Dr. Philip Arena, director of medical imaging at Harvard Vanguard Medical Associates and clinical professor of radiology at Boston University School of Medicine; Victoria Moceri, a Ph.D. candidate in epidemiology at the UW; and Sarah Polk, a premedical student.

The research was supported by Yale University’s Claude Pepper Aging Center, the American Cancer Society, the Robert Wood Johnson Foundation and the Harvard Pilgrim Health Care Foundation. Harvard Pilgrim Health Care, a not-for-profit health plan, has 1.3 million members in Massachusetts, Rhode Island, New Hampshire and Maine.