mammography, more harm than benefit
The belief that early diagnosis of cancer can save your life is deeply ingrained in the North American population. As a result, screening programs, especially for cancer of the breast and prostate, are widely supported by the health professions and the public. But an uncomfortable fact has now emerged — the potential benefit is very small indeed in relation to the large amount of harm caused.
Screening, don’t forget, involves subjecting normal healthy people to tests looking for disease. It does refer to patients with symptoms.
Screening with mammography for breast cancer and prostate-specific antigen (PSA) testing for prostate cancer can, and often does, make the cancer diagnosis before any symptoms appear. But unless the eventual cancer death rate is lower in screened people, the only result, other than the adverse consequences, is an increase in the length of time that the patient knows that they have the disease.
It is now clear that public appeals for women to get mammograms were based on grossly exaggerated promises of benefit.
Many women will remember the television and magazine advertisements suggesting that “if you are over 35 and haven’t had a mammogram, you need more than your breasts examined.” We now have two generations of women who believe regular mammography is essential for health, with widespread publicly financed programs.
Although PSA screening for prostate cancer has not been adopted as public health policy in Canada, it too is widely used and recommended.
How do the facts shape up in relation to this kind of public information? How many women’s lives are saved by mammography?
The recent analysis of the evidence from multiple studies shows that if 2, 000 women are screened with mammograms regularly for 10 years, only one life will be “saved” (that is, prolonged).
For prostate cancer, the story is similar in two large, long-awaited studies recently completed. In one, there was no benefit whatsoever from PSA screening and, in the other, 1,410 men had to be screened and 48 treated to prevent a single cancer death.
In view of this slim evidence on the benefit side, we must look closely at the harms caused by screening.
Half of all women screened regularly over a 10-year period will experience at least one false positive episode, meaning the mammogram showed something “suspicious” leading to repeat X-rays, other studies such as ultrasound and even biopsies and surgery of the breast. The anxiety caused by a false positive test has been well-documented.
False negative results also occur, with one in 10 breast cancers missed by the test.
For men, a positive PSA test is likely to lead to a biopsy of the prostate gland that may lead to a “cancer” being diagnosed that may or may not represent a real disease for the patient. This is frequently followed by a recommendation for major surgery carrying a significant risk of causing impotence and incontinence.
The most serious adverse effect of screening for breast and prostate cancer is that we are discovering thousands of people with what looks like a cancer under the microscope, but who would never subsequently develop any disease.
This is a relatively new revelation about breast cancer, but it has been known for decades prostate “cancer” can be found in 80 per cent of elderly men who have died of unrelated causes.
It is bad enough to be wrongly labelled with a malignant disease but the consequent cancer treatments are worse, causing harm to a person who had no medical problem in the first place.
This information is likely to cause dismay among health-care professionals and the public in view of the previous hope and promise of these screening procedures in the fight against cancer and the large industry we have built to support it involving physicians, nurses, technologists, support staff and equipment manufacturers, all with powerful, if understandable, vested interests.
At the very least, people attending for these tests should be given full and accurate information, rather than the current hype, and screening organizations must revise their recruitment processes. A decision to undergo screening or not, like any other medical procedure, should be made only after an explanation of the potential benefit and harm in easily understood terms.
Public education on this issue is already underway — witness the recent articles in news media about the change in guidelines from the United States Preventive Services Task Force and the American Cancer Society.
The process of changing professional practice and public perception will be long and difficult, but surely we cannot continue to promote screening tests that are now known to cause substantially more harm than benefit.
Charles Wright, a health services consultant, spent most of his career in academic and clinical surgery. Currently, he is a member of the Ontario Health Technology Advisory Committee and serves on the board quality of care committees at Cancer Care Ontario and the University Health Network in Toronto.
Winnipeg Free Press
Sat Dec 5 2009
Page: H1
Byline: Dr. Charles Wright
Follow us on: