There is much talk these days about the need to practise "evidence-based medicine."
That may seem self-evident - after all, if medical practice is not based on evidence then what is it based on: Intuition? Tradition? Politics? Emotion? Wishful thinking? Pecuniary gain?
Sadly, too often the answer to those questions is: "Yes."
Let's take a current, politically charged, emotionally laden issue as an example: mammography.
This week, the U.S. Preventive Services Task Force issued new recommendations on how mammography should be used to screen women for breast cancer. The blue-ribbon panel of experts said:
Women aged 50-74 should get mammograms every two years.
Mammograms are not recommended for women under 50 or for those 75 and older.
There is no additional benefit to be gained from clinical breast examination in women who undergo mammography.
There is no evidence that breast self-examination is useful.
There is no additional benefit gained from screening using digital mammography or magnetic resonance imaging (MRI), instead of traditional film X-ray mammography
(The recommendations apply to the general population, not to those at high risk because of a family history of breast cancer or who have tested positive for the breast cancer genes BRCA1 or BRCA2.)
Predictably, the USPSTF recommendations have caused an uproar, one that has spilled across the border, even though they mirror long-standing policies in most Canadian provinces.
Until now, U.S. health authorities have promoted annual mammography from age 40 and embraced ever-more expensive high-tech methods. In the United States, mammography is a big, profitable business.
The assumption, of course, is that earlier screening is better and that the newer the technology, the better. If only it were so simple.
Cancer screening, and breast-cancer screening in particular, has become a religion.
So the response to the USPSTF recommendations - which essentially challenge the current faith-based approach - has been zealous.
There are assertions that implementing these recommendations will deny women essential health-care services, rob young women of the opportunity of early detection and lead to thousands of needless deaths.
According to the USPSTF recommendations, published in the current issue of the Annals of Internal Medicine, that is not what the evidence tells us.
In fact, what the data say about the benefits of mammography is humbling.
USPSTF statistics indicate that in women aged 40 to 49, screening results in a relative risk reduction of 15 per cent; in women 50-59, it is 14 per cent; in those 60-69, 32 per cent and in women over 70, 12 per cent. There is little evidence of reduction in death in women over 75.
Even a cursory glance at those numbers will have people saying: Hold on, mammography actually benefits the 40-49 age group more than the 50-59 group.
That is true, relatively speaking, except for a key consideration - the risk of breast cancer increases with age.
In women under 50, it is 1 in 69; in those 50-59, 1 in 42; and in the 60-69 group, 1 in 29.
If you take a low risk and make it relatively smaller - which is what you do with mammography beginning at 40 - it doesn't save many lives.
To better understand, let's look at the numbers in a different way - the number needed to screen to reduce mortality.
Mammography programs would have to screen 1,904 women aged 39-49 for a decade to prevent a single death; in women aged 50-59, they would need to screen 1,339 for 10 years to prevent one death; and in women 60-69, for every 377 screened for a decade one death will be averted.
We cannot ignore, either, that screening not only has benefits, it can cause harm. Younger, premenopausal women have denser breasts and they have far more false-positive results, leading to unnecessary biopsies that are physically painful and psychologically damaging, not to mention the additional exposure to radiation.
Clearly, according to the evidence, the greatest benefit comes from screening women in the vulnerable 60-69 age group, followed by those in the 50-59 group. Screening those aged 40-49 entails tremendous expense with a modest return.
Naturally, consumer groups, many treating physicians and patients (particularly those whose breast cancer was detected before age 50) are outraged by this heartless analysis.
But there are many conflicting demands for scarce health-care doctors, so rational choices are required, no matter how politically unpopular.
Mass screening programs should not be determined by anecdote and wishful thinking.
Health-care decisions, personal and collective, should be based on evidence, regardless of how displeasing that evidence may be.
Erratum
Last week's column about the need to vaccinate seniors against H1N1 was supposed to include the sentence: "As proud veterans - so many of them now frail and elderly - stood yesterday in Remembrance Day ceremonies, one could not but be awed by their sacrifice and their stoicism." But the word "but" was omitted, making me look like, well, a butt. My apologies.
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SCREENING PROGRAMS
A new report from the U.S.
Preventive Services Task Force recommends that mammography to screen for breast cancer be done every two years for women aged 50-74. Many consumer groups are outraged by the recommendation, saying lives can be saved with annual screening programs that begin at age 40.
The Canadian Cancer Society endorses screening mammography for women aged 50-69 but each province has different criteria.
This list provides the age of eligibility and access for each of the provincial and territorial mammography screening programs.
British Columbia: 40; women can self-refer.
Alberta: 40; women can self-refer.
Saskatchewan: 50; women can self-refer.
Manitoba: 50; women can self-refer.
Ontario: 50; women can self-refer
Quebec: 50; doctor's referral.
New Brunswick: 50; women can self-refer.
Nova Scotia: 40; women can self-refer.
Prince Edward Island: 50; women can self-refer.
Newfoundland: 50; women can self-refer.
Northwest Territories: 40; women can self-refer.
Yukon: 40; women can self-refer.
Nunavut: It does not yet have an organized screening program.
Source: Canadian Breast Cancer Foundation