Errors in Conduct of the CNBSS Trials of Breast Cancer Screening Observed by Research Personnel

Objective To investigate why the Canadian National Breast Screening Study (CNBSS) did not show mortality reduction with mammography. This study explored long-standing concerns related to the validity of the randomization process, methods of recruiting women to participate in the trials, and training of the staff working in the CNBSS. Methods Surviving former CNBSS personnel, whose roles involved direct recruitment, enrollment, randomization, clinical examination, image interpretation, and management of patients in the CNBSS were interviewed. Individuals were contacted and consented to provide firsthand accounts of daily operations and adherence to research protocols via standardized questions. Consistency of observational data with quantitative results from the CNBSS trials was evaluated. Results Twelve of 29 (41.4%) staff confirmed that women with preexisting symptoms of breast cancer were systematically recruited at some centers; 55.2% (16/29) confirmed that personnel performing screening in CNBSS had very limited training and experience; 37.9% (11/29) verified that imaging equipment was often substandard; 48.3% (14/29) indicated that mammography image quality was generally poor; and 27.6% (8/29) corroborated that in some cases surgeons were unwilling to perform biopsies or surgeries for women with suspicious abnormalities found only on screening mammography that lacked a palpable correlate. Conclusion These firsthand accounts provide new information confirming that the CNBSS did not consistently and rigorously assess the true efficacy of screening mammography. The staff accounts clarify reasons why the CNBSS results were outliers compared with the six other randomized trials of screening mammography and should not be used as credible scientific evidence to inform health policy.

Automated summary

This study investigates the reasons why the Canadian National Breast Screening Study (CNBSS) did not demonstrate a reduction in mortality with mammography. It reveals concerns related to the validity of the randomization process, methods of recruiting women for the trials, and the training of CNBSS staff. Interviews with former CNBSS personnel confirm the presence of systematic recruitment of women with preexisting breast cancer symptoms, inadequate training and experience of the screening personnel, substandard imaging equipment, poor quality of mammography images, and reluctance of surgeons to perform biopsies or surgeries for women with suspicious abnormalities found only on screening mammography. These accounts highlight the inadequacy of CNBSS in assessing the efficacy of screening mammography and emphasize the need to consider the evidence from other randomized trials.