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The Mammography Dilemma: A Crisis for Evidence-Based Medicine?
- Steven N. Goodman, MD, MHS, PhD
The newest contretemps over mammography is yet the latest eruption from a debate that has been simmering for decades, boiling over at regular intervals onto the front pages of newspapers, the floors of Congress, and the laps of expert panels (1). But a closer look at this controversy, which is officially joined here by publication of the rationale for the recommendations of the U.S. Preventive Services Task Force (USPSTF) (2), shows that its focus has shifted in a way that poses a dilemma not only for women and their doctors, but for evidence-based medicine itself.
The debate in the 1990s was mainly about the advisability of screening women younger than 50 years of age; for older women, the benefits of mammography were thought to be certain. But the current debate has a new component, introduced by the findings of two Danish researchers, Olsen and Gøtzsche. Their review appeared last December in three forms: a brief summary in The Lancet(3); a version in the Cochrane Collaboration's Database of Systematic Reviews (4); and a more thorough version, including data on surgery rates, on the Lancet Web site (5). Some of their findings moved two prominent U.S. groups—the National Cancer Institute's PDQ (Physician Data Query) Advisory Board (http://nci.nih.gov/cancer_information/pdq) and the National Breast Cancer Coalition (http://www.natlbcc.org)—to soften their recommendations on mammography.
Olsen and Gøtzsche claimed some of the numbers they found indicated that postrandomization exclusions, baseline imbalances, and unblinded cause-of-death attributions had introduced bias into the existing mammography trials (6). The last factor led them to focus on deaths from all causes rather than breast cancer alone, decreasing bias but also guaranteeing that they would have trouble statistically discerning a small breast cancer effect (7). In the end, Olsen and Gøtzsche designated only the Canadian National …
