R. Scott Braithwaite, MD, MS
Potential Conflicts of Interest: None disclosed.
Braithwaite R.; Comments and Response on the USPSTF Recommendation on Screening for Breast Cancer. Ann Intern Med. 2010;152:539-540. doi: 10.7326/0003-4819-152-8-201004200-00201
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Published: Ann Intern Med. 2010;152(8):539-540.
TO THE EDITOR:
The USPSTF update of screening mammography recommendations (1) created controversy because many people feared it was motivated by cost containment rather than scientific evidence (2). However, neither the Task Force nor the underlying studies considered costs or cost-effectiveness (3, 4). It is tempting to attribute this misunderstanding to unfortunate timing: The USPSTF, a government-appointed body, recommended against routine mammography at a time when the government's role in controlling health spending was being widely debated. However, the true culprit behind misinterpretation may be more subtle. The metric underlying the USPSTF decisions, number needed to screen (NNS), obscures the rationale of subsequent decisions.
A decision based on NNS has many potential rationales. An unfavorably high NNS can argue against screening, because harms exceed benefits; the risk–benefit ratio is “too close to call” (either from a population or from an individual perspective); or benefits exceed harms, but not by enough to justify expenditures. The first 2 rationales do not consider cost, whereas the third rationale does. Because NNS-based decisions can be attributed to many rationales, NNS invites misinterpretation. Furthermore, no NNS threshold is universally favorable or unfavorable. An NNS of 10 (usually favorable) may be unfavorable if the harms and costs of screening are substantial but the benefits are slight. Conversely, an NNS of 10 000 (usually unfavorable) may be favorable if the harms and costs of screening are minimal but the benefits are substantial.
The USPSTF revised recommendations for women aged 39 to 49 years because the NNS of mammography increased to 1904 (1), a number that is usually unfavorable. The likely rationale was that risk–benefit ratio was too close to call, particularly on an individual patient basis. For women who attach great value to avoiding consequences of false-positive results (for example, biopsies and their potential complications or anxiety), harms may exceed benefits. However, for women who attach little value to avoiding these consequences, benefits may exceed harms. Accordingly, the USPSTF advised neither in favor of routine mammography (grades A or B) nor against it (grade D), but rather advised individualized decision making (grade C). However, because the USPSTF's rationale was implicit, it was misinterpreted. Many assumed the USPSTF was using NNS as a backdoor to rationing.
When expert groups invoke NNS to recommend against routine screening, they should specify their rationale, especially given current sensitivities about rationing. Misattributing a recommendation to cost rather than risk–benefit ratio wastes a teachable moment on how screening can cause harms and may erode the toehold of evidence-based medicine in the U.S. health care system.
R. Scott Braithwaite, MD, MS
New York University School of Medicine
New York, NY 10016
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