The journal Lancet recently published an important analysis from six physicians at Weill Cornell Medical College (359:404-406, 2002), rebutting an article published in an earlier issue of Lancet (358:1340-1342, 2001) that cast doubt on the value of mammography in preventing death from breast cancer. The Weill Cornell authors believe the debate over breast cancer screening has been misguided and has done a disservice to the general public, to physicians, and to women specifically. Their hope was that their latest analysis would reopen and refocus the issue. Indeed, the ensuing debate has had experts repeatedly change their stand on the value of mammography screening.
The Weill Cornell team, led by Drs. Claudia Henschke and David Yankelevitz of the department of radiology and Dr. Olli S. Miettinen of the department of medicine, pointed out the fundamental flaws in the design of the study that evaluated the usefulness of mammography screening. One flaw was the mistaken assumption that screening is supposed to prevent death from cancer almost immediately after it is performed. In reality, the authors noted, only early treatment can result in immediate cure, whereas the screening-prevented death would have occurred several years later.
Another even more fundamental flaw was the failure to include any meaningful measure of the screening’s usefulness. The purpose of screening for cancer is to enhance its curability and, thereby, to reduce the risk of death from the cancer insofar as it develops. This risk is expressed by the cancer’s case-fatality rate.
Thus, an important measure of any cancer screening’s usefulness is its resultant proportional reduction in the cancer’s case-fatality rate. The magnitude of this reduction can be estimated from trials (screening vs no screening, rather than early vs late treatment) only if they involve sufficiently long-term screening, and an appreciation of the time lag between cure and the thereby prevented deaths.
Drs. Ole Olsen and Peter C. Gøtzsche were the original authors of the Lancet meta-analysis that reviewed seven trials of mammographic screening and concluded that "there is no reliable evidence that screening for breast cancer reduces mortality." This conclusion was widely noted and publicized. On December 9, 2001, The New York Times said that "experts and women’s health advocates . . . do not know what to think about the report." More recently, another article in the Times reported that, "An independent panel of experts said today that there was insufficient evidence to show that mammograms prevented breast cancer deaths."