The use of computer-aided detection in clinical practice has increased since the FDA approved the technology and Medicare began reimbursing for its use. In our observational study of large numbers of community-based mammography facilities and patients, the use of computer-aided detection was associated with increases in potential harms of screening mammography, including higher recall and biopsy rates, and was of uncertain clinical benefit.
As others have reported,9,11–14
we found that the use of computer-aided detection was associated with higher recall rates than nonuse, implying that rates of false positive results were also higher with use, since most recalls do not result in a diagnosis of cancer. Increased recall rates and rates of false positive results may be logical consequences of the design of computer-aided detection software. With the goal of alerting radiologists to overlooked suspicious areas, computer-aided detection programs insert up to four marks on the average screening mammogram.13,27,28
Thus, for every true positive mark resulting from computer-aided detection that is associated with an under-lying cancer, radiologists encounter nearly 2000 false positive marks.29
Increased recall rates could be a necessary cost of improved cancer detection. The use of computer-aided detection was associated with a nonsignificant trend toward increased sensitivity but with no substantive change in the overall detection of cancer. Use of the technology was, however, more strongly associated with the detection of ductal carcinoma in situ than with the detection of invasive breast cancer, a finding that may stem from the propensity of computer-aided detection software to mark calcifications.5,30–32
To the extent that ductal carcinoma in situ is a precursor to invasive cancer,33
the greater percentage of cancers found that were ductal carcinomas in situ after the implementation of computer-aided detection than before implementation may be viewed optimistically as a shift toward detecting breast cancer at an earlier stage with the use of computer-aided detection. On the other hand, the natural history of ductal carcinoma in situ is certainly more indolent than that of invasive cancer,34
and the effect of computer-aided detection on mortality from breast cancer may be limited if it chiefly promotes the identification of ductal carcinoma in situ rather than invasive cancer.35
No single measure is sufficient to judge the effect of computer-aided detection on interpretive performance.36
Rather, the benefits of true positive results must be weighed against the consequences of false positive results, including associated economic costs. Our results suggest that approximately 157 women would be recalled (and 15 women would undergo biopsy) owing to the use of computer-aided detection in order to detect one additional case of cancer, possibly a ductal carcinoma in situ (see the Supplementary Appendix
, available with the full text of this article at www.nejm.org
). After accounting for the additional fees for the use of computer-aided detection37
and the costs of diagnostic evaluations after recalls resulting from the use of computer-aided detection,38
we calculated that system-wide use of computer-aided detection in the United States could increase the annual national costs of screening mammography by approximately 18% ($550 million) (see the Supplementary Appendix
Facilities that adopted computer-aided detection had performance measures before its implementation that differed from those at facilities that never adopted computer-aided detection; these differences were consistent with differences in the characteristics of patients and radiologists at the two groups of facilities. The use of computer-aided detection may have caused a regression toward mean levels of performance among radiologists whose interpretations of mammograms tended to differ from those of most radiologists, but its implementation was associated with changes in specificity and recall rates that overshot levels at facilities that never implemented computer-aided detection. Moreover, the use of computer-aided detection remained significantly associated with decreased specificity, decreased positive predictive value, and decreased overall accuracy in analyses that adjusted for differences in characteristics of patients, radiologists, and facilities. Nevertheless, the association between the use of computer-aided detection and the observed changes in performance could be explained by factors we did not measure.
Although six of the seven facilities that adopted computer-aided detection reported using it for 100% of mammograms after implementation, we did not measure the use of computer-aided detection at the level of the individual mammogram. In this respect, our estimates of the effects of computer-aided detection on performance may be conservative. All facilities that implemented computer-aided detection used the same commercial product. The manufacturer has updated its detection software since 2002, but we are unaware of any community-based studies that have found improved detection of breast cancer with recent versions of the software.
Even in our large study, only 156 cases of cancer developed during the study among women screened at facilities using computer-aided detection, resulting in wide confidence intervals around estimates of sensitivity and cancer-detection rates after implementation. Because of the rarity of breast cancer in community samples, very large samples would be needed to study the effect of the use of computer-aided detection on sensitivity with high statistical power (approximately 750,000 mammograms interpreted in total, half with the use of computer-aided detection and half without).
In conclusion, we found that, among large numbers of diverse facilities and radiologists, the use of computer software designed to improve the interpretation of mammograms was associated with significantly higher false positive rates, recall rates, and biopsy rates and with significantly lower overall accuracy in screening mammography than was nonuse. The nonsignificant trend toward greater sensitivity with the use of computer-aided detection as compared with nonuse may be largely explained by increased detection of ductal carcinoma in situ. As an FDA-approved technology whose use can be reimbursed by Medicare, computer-aided detection has been incorporated quickly into mammography practices, despite tentative evidence of clinical benefits. Now that computer-aided detection is used in the screening of millions of healthy women, larger studies are needed to judge more precisely whether benefits of routine use of computer-aided detection outweigh its harms.