Computer-Aided Detection Reduces the Accuracy of Mammograms
Computer-Aided Detection (CAD) that uses software designed to improve how radiologists interpret mammograms may instead make readings less accurate, according to new research. Use of CAD did not clearly improve the detection of breast cancer. The research was conducted by investigators at the University of California Davis Health System, Sacramento, Calif., and colleagues in the Breast Cancer Surveillance Consortium, which is sponsored by the National Cancer Institute (NCI), part of the National Institutes of Health.
The results of the study show that women who got screening mammograms at centers using CAD devices were more likely to be told their mammogram was abnormal and thus undergo a biopsy to rule out breast cancer. Findings appear in the April 5, 2007 issue of the New England Journal of Medicine and were funded by NCI, the Agency for Healthcare Research and Quality, and the American Cancer Society.
CAD software analyzes the mammogram image and marks suspicious areas for radiologists to review, thus assisting them in determining which images could lead to invasive tumors. CAD was approved by the U.S. Food and Drug Administration in 1998 and has been incorporated into many mammography imaging practices, but its effect on the accuracy of interpretation has been unclear.
"This study points out the need for the use of other techniques to find cancer at its earliest stages. NCI is incorporating techniques for imaging at the molecular level into many of its studies and is also conducting studies to improve the use of CAD and conventional mammography," said John E. Niederhuber, M.D., NCI Director. "In the end, technology facilitates screening. Ultimately, treatment requires radiologists working with the examining physician and the responsible surgeon to put everything together. We worry about false positives, but we certainly don't want to miss any cancers, either."
Investigators looked at the use of screening mammography in 222,135 women who had 429,345 mammograms. The period of observation was from 1998 through 2002 and took place at 43 facilities in Colorado, New Hampshire, and Washington states. The study included 2,351 women who received a diagnosis of breast cancer within one year after screening and also received a mammogram that did or did not use CAD.
"Within three years of FDA approval, 10 percent of the mammography facilities in the country were using CAD," said lead researcher Joshua J. Fenton, M.D., UC Davis Health System. "There had been no large-scale community-based review of CAD efficacy despite the rapid adoption of this technology so we did this study to see if CAD was proving to be beneficial."
Seven facilities, representing 16 percent of the study sites, implemented computer-aided detection during the study period. With the use of CAD, 32 percent more women were recalled for more tests and 20 percent more women had a breast biopsy. Use of the software had no clear impact on the early detection of breast cancer. The study suggests that, if anything, the software may promote the detection of the least dangerous breast cancers, such as localized, in situ breast cancers. The effect of in situ cancers on breast cancer mortality remains unknown and some evidence suggests that not all develop into invasive cancers.
Every time the CAD software marks a real cancer, a radiologist has to consider about 2,000 additional false-positive marks, making it very difficult to distinguish between real cancers and those that are not cancer. The authors estimate that for every additional woman diagnosed with breast cancer on the basis of CAD, 156 women are falsely recalled for more tests and 14 had unnecessary biopsies to exclude cancer.
"It's unfortunate that the use of the software has proliferated so widely before we are certain of its benefits," said Fenton. "We need studies to determine if the benefits of the software outweigh its harms and costs. There is also the potential for new studies to improve the performance of CAD software."
The authors estimate that if all mammography facilities adopt CAD, the annual cost of mammograms in the United States could increase 18 percent, or an additional $550 million nationwide.
Fenton JJ, Taplin SH, et al. Influence of Computer-Aided Detection on Performance of Screening Mammography. NEJM, Vol. 356, No. 14. April 5, 2007.
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