Screening Mammography Would Have Been Initiated Regardless of the CNBSS

Abstract

I respectfully disagree with Drs. Jha and Ware’s concluding statement “The CNBSS is compelling enough to never start mammograms for breast cancer but not compelling enough to stop screening.” In addition, the assumption that “If the CNBSS was the first RCT in screening for breast cancer, it is unlikely that screening would have been approved” goes against our standard methods of critical review. Regardless of the order in which data are published, we still have an obligation as scientists to uphold rigorous methodology (1). Our clinical decisions are dependent upon this adherence to proper randomized controlled trial design. Drs. Jha and Ware describe the many problems with the Canadian National Breast Screening Study (CNBSS) including improper randomization, low sample size, and poor quality of mammograms. The problems significantly discount the validity of the study and call into question the results. A well-designed CNBSS would have had the results of the physical examination unknown to the personnel allocating patients to the screened group vs. the control group. Because the allocation was unblinded, a disproportionate number of advanced cancers were placed in the screening group resulting in poor outcomes. The CNBSS was not designed with enough statistical power to evaluate the benefit of screening in the two age groups (40–49 and 50–59). A tenet of quality research is to prospectively design the study to include enough patients to show statistical significance. This was not adhered to in the CNBSS (2). Finally, the poor quality of mammograms is a significant factor in patient outcome. The United States Congress recognized the importance of minimum standards. In an effort to make sure that facilities in the United States were conforming to providing quality mammography, the Mammography Quality Standards Act was passed in 1992 (3). This act requires facilities to maintain accreditation with submission of images to prove adequate image quality and to undergo annual Mammography Quality Standards Act administration. No other area in radiology has been held to the same expectations as mammography, underscoring the importance of high-quality imaging and the potential for variance at each site. It is widely recognized that poor-quality mammography leads to missed cancers. Missed cancers result in no change in mortality. To assume that we would have relied on the results of the CNBSS with the accompanying significant faults described previously, is misguided. A poorly designed study is a poorly designed study, regardless of the presence or absence of other published data.