10-YEAR RISK OF FALSE-POSITIVE SCREENING MAMMOGRAMS AND CLINICAL BREAST EXAMINATIONS

Background The cumulative risk of a false positive result of a breast- cancer screening test is unknown. Methods We performed a 10-year retro spective cohort study of breast-cancer screening and diagnostic evalua tions among 2400 women who were 40 to 69 years old at study entry. Mam mograms or clinical breast examinations that were interpreted as indet erminate, aroused a suspicion of cancer, or prompted recommendations f or additional workup in women in whom breast cancer was not diagnosed within the next year were considered to be false positive tests. Resul ts A total of 9762 screening mammograms and 10,905 screening clinical breast examinations were performed, for a median of 4 mammograms and 5 clinical breast examinations per woman over the 10-year period. Of th e women who were screened, 23.8 percent had at least one false positiv e mammogram, 13.4 percent had at least one false positive breast exami nation, and 31.7 percent had at least one false positive result for ei ther test. The estimated cumulative risk of a false positive result wa s 49.1 percent (95 percent confidence interval, 40.3 to 64.1 percent) after 10 mammograms and 22.3 percent (95 percent confidence interval, 19.2 to 27.5 percent) after 10 clinical breast examinations. The false positive tests led to 870 outpatient appointments, 539 diagnostic mam mograms, 186 ultrasound examinations, 188 biopsies, and 1 hospitalizat ion. We estimate that among women who do not have breast cancer, 18.6 percent (95 percent confidence interval, 9.8 to 41.2 percent) will und ergo a biopsy after 10 mammograms, and 6.2 percent (95 percent confide nce interval, 3.7 to 11.2 percent) after 10 clinical breast examinatio ns. For every $100 spent for screening, an additional $33 was spent to evaluate the false positive results. Conclusions Over 10 years, one t hird of the women screened had abnormal test results requiring additio nal evaluation, even though no breast cancer was present. Techniques a re needed to decrease false positive results while maintaining high se nsitivity. Physicians should educate women about the risk of a false p ositive result of a screening test for breast cancer. (C) 1998, Massac husetts Medical Society.