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False-Positive Screening Results for Breast Cancer
Am Fam Physician. 1998 Oct 1;58(5):1198.
The effectiveness of mammography for breast cancer screening has been documented by several randomized clinical trials. Most physicians also recommend annual breast examinations for female patients. Whether this latter practice is effective in the early diagnosis of breast cancer is unknown. The majority of recommendations call for women to undergo initial screening mammography at 40 years of age. Elmore and colleagues performed a retrospective cohort study of the cumulative risks of false-positive results on mammography and clinical breast examination in women screened over a 10-year period.
Women included in the study were members of Harvard Pilgrim Health Care, a large health maintenance organization based in New England. The subjects included women who were between the ages of 40 and 69 years on July 1, 1983. According to guidelines put forth by the health maintenance organization, these women were screened by breast examination and mammography every other year from ages 40 to 49 and annually beginning at age 50. Patients were excluded if they had a history of breast cancer, breast implants or prophylactic mastectomy. Most of the mammograms were performed at community or academic radiology centers, and all were read by board-certified radiologists.
In reviewing the data for mammography and clinical breast examinations, the diagnostic impressions were recorded as one of the following: normal; abnormal and probably benign; abnormal but indeterminate; or abnormal and suspicious for cancer. Recommendations for follow-up testing were reviewed, including second-opinion review of the films, repeat mammography within 12 months, ultrasonography, physical examination or biopsy. A test was classified as positive if it required follow-up testing. True-positive results were those in which a diagnosis of breast cancer was made on the basis of pathologic findings within one year of the screening tests. The remainder of patients who underwent additional investigations but did not have breast cancer were considered to be false positives.
A sample of 2,400 women were enrolled in the study. During this 10-year period, 9,762 screening mammograms were performed. The median number of mammograms for each patient was four, with a range of one to nine studies. The mammograms were read by a total of 93 radiologists.Also during the study period, 10,905 screening clinical breast examinations were performed by 381 health care providers.
A total of 88 breast cancers were diagnosed in the patient population, with 58 being detected by mammography. False-positive results on mammography occurred in 631 studies (6.5 percent) and in 402 breast examinations (3.7 percent). More significantly, the highest rates of false-positive mammograms (7.8 percent) and false-positive breast examinations (6.0 percent) were in women between the ages of 40 and 49 years. For these same women, the cumulative risks of a false-positive mammogram after five studies was 30.3 percent. For all patients, the cumulative risk of having at least one false-positive study after 10 screening mammograms was determined to be 49.1 percent, and for clinical breast examinations the risk of a false-positive result was 22.3 percent. The costs of further evaluations following false-positive screening were estimated to be $329,649.
The authors conclude that there is a considerably high rate of false-positive results with both screening mammography and clinical breast examinations. False-positive test results increase expenses significantly and add psychologic stress for patients. The authors propose having radiologists available on site to obtain more expedient work-ups of patients with abnormal mammograms. They also encourage educating patients about the risks of false-positive results before seeking screening examinations.
Elmore JG, et al. Ten-year risk of false positive screening mammograms and clinical breast examinations. N Engl J Med. April 16, 1998;338:1089–96.
Copyright © 1998 by the American Academy of Family Physicians.
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