Performance of diagnostic mammography differs in the United States and Denmark

Abstract

Diagnostic mammography is the primary imaging modality to diagnose breast cancer. However, few studies have evaluated variability in diagnostic mammography performance in communities, and none has done so between countries. We compared diagnostic mammography performance in community-based settings in the United States and Denmark. The performance of 93,585 diagnostic mammograms from 180 facilities contributing data to the US Breast Cancer Surveillance Consortium (BCSC) from 1999 to 2001 was compared to that of all 51,313 diagnostic mammograms performed at Danish clinics in 2000. We used the imaging workup's final assessment to determine sensitivity, specificity and an estimate of accuracy: area under the receiver-operating characteristics (ROCs) curve (AUC). Diagnostic mammography had slightly higher sensitivity in the United States (85%) than in Denmark (82%). In contrast, it had higher specificity in Denmark (99%) than in the United States (93%). The AUC was high in both countries: 0.91 in United States and 0.95 in Denmark. Denmark's higher accuracy may result from supplementary ultrasound examinations, which are provided to 74% of Danish women but only 37% to 52% of US women. In addition, Danish mammography facilities specialize in either diagnosis or screening, possibly leading to greater diagnostic mammography expertise in facilities dedicated to symptomatic patients. Performance of community-based diagnostic mammography settings varied markedly between the 2 countries, indicating that it can be further optimized.

Figure 1

Diagnostic mammography empirical receiver operating characteristic (ROC) curves for Denmark and the United States, respectively. Empirical or observed sensitivity is plotted against the empirical or observed false-positive rate (1 minus specificity) for each BI-RADS^© (Breast Imaging Reporting and Data System) criterion point. Starting from the lower left, the cut points for the mammographic examination BI-RADS™ assessments being called positive are 5, 4, 3, 2, and 1. AUC is area under the ROC curve.