When first introduced four decades ago, breast cancer screening with mammography was widely regarded as an important tool in the fight against a terrible disease. It seemed obvious that the earlier it could be diagnosed the more lives could be saved. Aggressive treatment, it was thought, would prevent the cancer from spreading through the body. A huge amount of research evidence since then has slowly and painfully led to a different conclusion.
It is now clear that the benefits of screening mammography have been greatly exaggerated and the serious adverse effects all but ignored in the enthusiasm to support breast screening programs. It's time for these programs to be reconsidered.
It must be emphasized that this is the case for population screening of healthy women, not those with extra high risk factors.
This is a very unpleasant message for modern developed societies where three generations of women have been led to believe that regular mammograms will save their lives and where an enormous related industry has been built up, but it is time to face the facts.
Unscientific opinions and powerful vested interests abound on this subject, so it is essential to focus on well-conducted studies from independent sources to summarize the evidence. One of the most trusted of these, the Cochrane Collaboration, has been studying screening mammography intensively. Its most recent bulletin states that the benefit of screening 2,000 women regularly for 10 years is that one woman may have her life prolonged. Of the other 1,999 women, at least 200 will have false positive mammograms leading to biopsies and surgery, and at least 10 women will be falsely diagnosed with breast cancer and consequently subjected to unnecessary surgery, radiotherapy and chemotherapy.
This problem, called over-diagnosis, occurs when a biopsy reveals microscopic cells that are currently labeled as "cancer" by the pathologist, but with uncertain potential to cause any significant problem for the patient in the future. The "c" word inevitably causes fear and distress for the patient and an aggressive treatment plan from the doctors. This is now widely recognized, even by the U.S. National Cancer Institute which has recently recommended that these uncertain "cancers" should instead be labeled "IDLE" (indolent lesions) until research can help us differentiate those that need treatment from those that do not.
Now we have more evidence. The Canadian National Breast Cancer Screening Study published this week in the British Medical Journal, and widely reported in the international media, solidly confirms that there is no upside to breast screening healthy women in terms of mortality benefit in exchange for the downside of all the adverse consequences. In this study, 90,000 women aged 40-59 were randomly allocated to the mammography screening program or to annual physical examination only, with follow up to 25 years. The mortality was the same in both groups (500 in the first group and 505 in the second).
Adverse consequences from screening can include false negatives (a cancer is growing but missed by the mammogram), and potentially cancer-causing cumulative X-ray exposure. Not to mention the anxiety, pain and discomfort that women experience with the procedure and the huge cost of these programs to the health care system.
This new study, along with the Cochrane analysis, represent the beginning of a growing consensus among scientists and clinical epidemiologists that the evidence no longer supports population screening of healthy women with mammography. Several prominent female U.K. doctors have gone public about choosing not to have breast cancer screening, including the editor of the BMJ, the past president of the Royal College of GPs, and the professor of obstetrics at King's College London.
Nobody can be happy about all of this disappointing news with its serious public, professional and political implications, but surely we cannot ignore it. The hope that breast screening could cause a reduction in the mortality from this terrible disease was at first well placed 40 years ago, but it is no longer possible to advocate for an intervention that carries such a tiny (if any) likelihood of benefit along with such a huge burden of harmful consequences.
The very essence of science is about seeking truth through the constant cycle of evidence, analysis and revision. In response to a hostile question, John Maynard Keynes famously remarked "When the facts change, I change my mind. What do you do, sir?" We should heed that lesson here.
It may take a long time to dispel the false hope that has been given to women with mammogram screening, but the very least and immediate response should be the development of a mandatory consent form for women to sign before screening that distinguishes the most recent and overwhelming evidence from the current inappropriate enthusiasm. Women would then be empowered to make an informed choice.
Public health agencies should also consider a comprehensive plan for public re-education about screening mammography, followed by the gradual dismantling of population breast screening programs across the country.
Following Dr. Charles Wright's career as surgeon, teacher, researcher and health system administrator, he is now a consultant in medical affairs, program planning and evaluation based in Toronto, and an expert advisor with EvidenceNetwork.ca. He recently stepped down as chair of the Ontario Health Technology Advisory Committee.