Breast Cancer Screening: The Controversy and the Evidence
Breast cancer found by trained hands of nurses equivalent to mammograms in a study of 89,000 Canadian women. Result disrupts current US beliefs
For 25 years the breasts of 89,000 Canadian women were examined either by mammograms (x-ray) or by nurses trained to perform skilled clinical (manual) breast exams. Canadian women were randomly assigned to one of these two examination procedures. The surprising result disrupted current beliefs because the number of breast cancers detected by the nurses were the same as those detected by radiologists using mammograms. The study also reported that 22% of the “cancers” mammograms were “overdiagnosed”, false positives. Although the final report was challenged by radiologists who use mammograms, the results have not been invalidated. An update in 2016 found that the rate of false positives, overdiagnoses was significantly higher than first observed.
The finding, that skilled clinical breast exams coupled with self-exam training are as effective in detecting breast cancer as mammograms, is disruptive because it contradicts common beliefs and current practices. The evidence also challenges US government appointed agencies that set national guidelines for breast cancer screening and influential private organizations that advise women and practitioners.
The latest breast cancer screening recommendation from a leading private agency, the American Cancer Society are instructive in this regard.
The American Cancer Society’s puzzling response.
The American Cancer Society (ACS) recently issued a new guideline endorsing mammograms as the exclusive means to screen women for breast cancer along with an oddly worded “qualified” recommendation for clinical breast exams*. ACS’ published recommendation for mammograms overlooked the landmark Canadian study, although the it was referenced in ACS’ unpublished report.
The ACS indicated that they based their new guideline on an “evidence review“. But their published, widely promulgated position excluded contradictory findings as well as a growing body of evidence about how cancer is first detected.
The ACS decision to bypass knowledge that disrupts their guideline is troubling. But more troubling is their advice to millions of women to submit to radiological screening exams that have been demonstrated to be more costly and more invasive, but not more effective than the hands of nurses and patients trained to perform breast exams.
The accuracy of both mammograms and clinical (manual) breast exams depend on the quality of the examiners’ skills
Well designed studies also find that breast cancer detection accuracy depends on the competencies of the examiner as well as the method used. Mammograms are read (viewed) by clinicians whose accuracy depends on their training and development of visual discrimination skills whereas the accuracy of clinical breast exams depends on training the sense of touch and development of palpation skills.
Research reports wide variations in the accuracy among radiologists interpretations of mammograms. Training and experience are found to improve radiologists’ diagnostic accuracy. Similarly, studies of clinicians (and women) trained to perform manual breast exams demonstrate significantly greater accuracy in detecting small suspicious breast tumors and fewer false positive “detections” than those who are untrained.
Why is evidence ignored?
In science and medicine a period of resistance typically results when evidence contradicts established traditions and beliefs even when the practices or beliefs are ineffective or worse. This was dramatically demonstrated when an effective new treatment for stomach ulcers was rejected for nearly a decade by experts and by US health officials. In the present, far more potentially deadly case of breast cancer screening.
There is much resistance to the discovery that mammograms are not superior to trained hands in Canada. One notion advanced to explain the lack of discrepancy is that Canadian mammography machines are older than those in the US. But this argument lacks credibility because the image quality and resolution of x-ray mammography has not changed in more than 50 years. Moreover, images produced by newer digital mammograms do not improve the resolution or clarity of film x-ray.
So what should the American Cancer Society do now to advise women?
ACS should review, revise and update their breast cancer screening recommendations including relevant evidence that was overlooked.
Mark Kane Goldstein, Ph.D.
The MammaCare Foundation