Long-term risk of false-positive screening results and subsequent biopsy as a function of mammography use.

PURPOSE To retrospectively determine the long-term risk of false-positive mammographic assessments and to evaluate the effect of screening regularity on the risk of false-positive events. MATERIALS AND METHODS Institutional review board approval was obtained, and informed consent was waived. Retrospective analysis was performed for the occurrence of false-positive assessments among 83,511 women who underwent 314,185 mammographic examinations from January 1, 1985, to February 19, 2002. Data were collected from a database that had been assembled prospectively. Two categories of false-positive events were examined: biopsies that did not reveal cancer and false-positive mammographic assessments. Rates of false-positive events were compared by using a chi2 analysis, and 95% confidence limits were calculated. Because comparisons of multiple pairs were considered, all P values that demonstrated statistical significance exceeded the requirement of the Bonferroni correction. RESULTS While the overall rates of biopsies that did not reveal cancer and of false-positive mammographic assessments were similar to those found in other studies, most of the burden of false-positive events was borne by women who underwent intermittent screening. Long-term rates of false-positive events were lower among women who underwent regular screening than among those who underwent intermittent screening. In the 5-year group, 2.9% of women who underwent five mammographic examinations over the next 5 years had biopsy results that did not reveal cancer, whereas 4.6% of women who underwent three mammographic examinations over the next 5 years had biopsy results that did not reveal cancer. For women who underwent regular screening, the risk of undergoing biopsies that did not reveal cancer declined over time to 0.25% per year after several years of screening, a value that is lower than the risk of these events among women who did not undergo screening. The rate of false-positive mammographic assessments was also lower for women who underwent regular screening than for those who underwent intermittent screening. CONCLUSION Prompt annual attendance for mammographic screening reduces the occurrence of false-positive mammographic results.