Predicting the cumulative risk of false-positive mammograms

Background: The cumulative risk of a false-positive mammogram can be substa ntial. We studied which variables affect the chance of a false-positive mam mogram and estimated cumulative risks over nine sequential mammograms. Meth ods: We used medical records of 2227 randomly selected women who were 40-69 years of age on July 1, 1983, and had at least one screening mammogram, We used a Bayesian discrete hazard regression model developed for this study to test the effect of patient and radiologic variables on a first false-pos itive screening and to calculate cumulative risks of a false-positive mammo gram, Results: Of 9747 screening mammograms, 6.5% were false-positive; 23.8 % of women experienced at least one false-positive result. After nine mammo grams, the risk of a false-positive mammogram was 43.1% (95% confidence int erval [CI] = 36.6%-53.6%). Risk ratios decreased with increasing age and in creased with number of breast biopsies, family history of breast cancer, es trogen use, time between screenings, no comparison with previous mammograms , and the radiologist's tendency to call mammograms abnormal. For a woman w ith highest-risk variables, the estimated risk for a false-positive mammogr am at the first and by the ninth mammogram was 98.1% (95% CI = 69.3%-100%) and 100% (95% CI = 99.9%100%), respectively. A woman with lowest-risk varia bles had estimated risks of 0.7% (95% CI = 0.2%-1.9%) and 4.6% (95% CI = 1. 1%-12.5%), respectively. Conclusions: The cumulative risk of a false-positi ve mammogram over time varies substantially, depending on a woman's own ris k profile and on several factors related to radiologic screening. By the ni nth mammogram, the risk can be as low as 5% for women with low-risk variabl es and as high as 100% for women with multiple high-risk factors.