Mammograms and clinical breast cancer exams produce high level of false-positive results

provided by Harvard Medical School

ver a ten-year-period, one out of three women who had screening mammograms and clinical breast exams had abnormal results that required additional testing even though no breast cancer was present, researchers at the University of Washington and Harvard Medical School have found. The study of false positives, abnormal results that turn out not to be cancer is published in the New England Journal of Medicine.

The researchers' interest in performing the study stemmed from the 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 one mammogram in 10 produces a false-positive.

They 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.

"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 Dr. Joann G. 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, instructor in ambulatory care and prevention 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 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.

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, the researchers believe..

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.

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.

Additional investigators are Dr. Suzanne Fletcher, professor of ambulatory care and prevention at Harvard Medical School; 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 is the largest not-for-profit health plan in New England. In independent surveys such as Newsweek and U.S. News and World Report, it has been rated among the best HMOs in the nation.