Blinded Comparison of Computer-Aided Detection with Human Second Reading in Screening Mammography: The Importance of the Question and the Critical Numbers Game

Abstract

1Department of Radiology, George Washington University, 2150 Pennsylvania Ave., NW, Washington, DC 20037. Address correspondence to R. F. Brem. he authors of the well-designed study reported in the previous article [1] set out to compare the use of computer-aided detection (CAD) and a single radiologist interpretation of screening mammography with double reading for the improved diagnosis of breast cancer. With the increasing use of CAD, as well as the ongoing controversy about its use, this is an important goal and the authors ask a critically important question. However, it is also a challenging goal. The comparison of single reading with CAD versus double reading requires a large patient population to achieve sufficient statistical power to definitively answer the question posed. The admirable study, reported in this issue of AJR [1], is the basis on which additional studies will continue to build our knowledge base of this rapidly expanding field. Although not the primary goal, additional and excellent insights about the use of CAD as well as its integration into clinical practice result from this study. The authors [1] have used sophisticated and extensive statistics. They report the recall rate, biopsy rate, positive predictive value, and increased cancer detection rates for a single reader with CAD as compared with the double reading of mammograms. In this study, 6,381 consecutive screening mammograms were included in which a total of 18 cancers were present, 15 diagnosed and three false-negative cancers that were found on imaging 1 year later. The literature reports between 3 and 8 cancers per 1,000 screening mammograms [2], although the prevalence of breast cancer in the population reported in the study being discussed is 2.03 per thousand for the primary reader and 2.35 for all three “readers,”—that is, the primary reader, the primary reader with CAD, or the primary reader along with the second human reader [1]. The authors ascribe this difference to the fact that these are predominantly incidence cancers and not prevalence cancers because most patients had prior mammograms and suggest that this difference likely reflects the excellent care afforded patients seen in the investigators’ clinical practice. Nevertheless, the result of the study of the 6,381 screening mammograms is 18 cancers. This is the primary limitation of this study. The authors note that the small study size does not allow for a statistical comparison. In fact, they state that “.... the number of cases was too small to determine if the CAD or if the human reader was superior,....” and therefore the question that this study set out to investigate could not be definitely answered. The authors understand the limitations of their study; they state that: