Breast Cancer Screening: The Controversy and the Evidence
On February 11, 2014 the world’s scientific and medical communities learned that trained hands find the same number of breast cancers as do mammograms.
For 25 years the breasts of 89,000 Canadian women were examined either by radiologists using mammograms or by nurses trained to perform skilled clinical (manual) breast exams. Women in the study were randomly assigned to be examined by the hands of nurses trained to perform clinical breast exams or by mammograms (x-rays of the breast) viewed by radiologists. The Canadian study reported there was no difference between the number of breast cancers detected by nurses trained hands and those detected by radiologists using mammograms. The study also reported that 22% of the mammograms were “overdiagnosed” or resulted in false positives. Although the final report was challenged by radiologists, the results have not been invalidated.
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, previous knowledge and current practices. The evidence also challenges the position of 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published recommendation for mammograms overlooked the landmark Canadian study, although the it was referenced in ACS’ unpublished report.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 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 visual discrimination skills whereas the accuracy of clinical breast exams depends on the sense of touch and palpation skills.
Research reports find wide variations in the accuracy of 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 evidence is 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
The ACS recommends that all women should become familiar with the potential benefits, limitations, and harms associated with breast cancer screening
Women with an average risk of breast cancer should undergo regular screening mammography starting at age 45 years. (Strong Recommendation)
1a. Women aged 45 to 54 years should be screened annually. (Qualified Recommendation)
1b. Women 55 years and older should transition to biennial screening or have the opportunity to continue screening annually. (Qualified Recommendation)
1c. Women should have the opportunity to begin annual screening between the ages of 40 and 44 years. (Qualified Recommendation)
Women should continue screening mammography as long as their overall health is good and they have a life expectancy of 10 years or longer. (Qualified Recommendation)
The ACS does not recommend clinical breast examination for breast cancer screening among average-risk women at any age. (Qualified Recommendation)
aA strong recommendation conveys the consensus that the benefits of adherence to that intervention outweigh the undesirable effects that may result from screening. Qualified recommendations indicate there is clear evidence of benefit of screening but less certainty about the balance of benefits and harms, or about patients’ values and preferences, which could lead to different decisions about screening.“