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andré picard

"Breast cancer screening saved my life" is one of the most powerful narratives in modern medicine, if not in Western culture more generally.

So no wonder the new Canadian recommendations on screening mammography – suggesting only postmenopausal women undergo the test and do so less often – have sparked anger.

Everyone knows a breast cancer survivor with an inspiring tale, just as everyone knows the mantra, "early detection saves lives."

If only repetition swathed in pink ribbons was all that was required to make it so.

All the committee members who produced the new guidelines had to work with was scientific evidence – and the evidence is a lot more equivocal than the anecdote and a lot more convincing than the dire warnings that "thousands will die" if the new recommendations are followed.

Here is a summary of the Canadian Task Force on Preventive Health Care guidelines on breast cancer screening:

* Canadian women 50 to 74 should have mammograms every two to three years, instead of annually from age 50 to 69 as per the earlier recommendation;

* Women under the 50 should not have mammograms at all;

* Women 70 to 74 should have mammograms every two to three years; screening was not previously recommended in this age group;

* Clinical breast examinations and breast self-examination have no benefit, so they are not recommended.

The Canadian guidelines would not apply to women who are at high risk (meaning they have a family history of breast cancer or have tested positive for the breast cancer genes BRCA1 or BRCA2). They are similar to those issued by the U.S. Preventive Services Task Force earlier this year.

In both countries, annual mammography for all women over 40 was becoming the norm. So why do the experts say that is not a good idea?

First and foremost because a growing body of evidence shows that screening is not the lifesaver it is made out to be.

While it is true that breast cancer mortality has fallen by about 30 per cent since screening programs began in the late 1980s, it is also true that rates were falling before screening. Awareness about breast cancer is the biggest factor – women no longer show up at the doctor's office with grapefruit-size tumours – and treatment has improved dramatically as well.

Breast cancer is on the rise because cancer is, above all, a disease of aging, and people are living longer. Screening has helped reduce mortality, but it is not a panacea.

A study published last month in the Archives of Internal Medicine featured some of the most humbling data to date. It showed that, while about 60 per cent of breast cancer cases are detected through screening programs, the screening benefited only 13 per cent of women (meaning their cancer would not have been detected and treated otherwise), and extended the lives of only 3 per cent.

Let's analyze those data in a more digestible fashion. About 23,400 Canadian women will be diagnosed with breast cancer this year and 5,100 will die.

The numbers in the archives study suggest that between 400 and 1,800 Canadian women will be helped by screening. That's a tiny fraction of the four million or so who have mammograms each year.

"I hate to have to say this, [but]… survivors are more likely to have been overdiagnosed than actually helped by the test," Gilbert Welch, a professor of medicine at Dartmouth College in Hanover, N.H., told The New York Times.

He likens screening to gambling, with big winners (those who will be saved from breast cancer) but many small losers (those diagnosed with cancer that is slow-growing and unlikely to kill or harm them).

That is because many women who undergo screening mammography have false positives (meaning they are told they may have breast cancer when they do not) and some are treated unnecessarily.

A study published in the Annals of Internal Medicine earlier this year found that, over a 10-year period, one in every two women who gets a mammogram will receive a false positive. Aside from the psychological impact of a cancer scare, one in 11 will actually be treated for breast cancer that does not require immediate treatment – undergoing biopsies, radiation and surgery.

The fundamental problem, aside from failing to recognize that screening carries risks as well as benefits, is the presumption that anyone who has had breast cancer detected by screening has survived because of the test.

That is simply not true.

That's because there are different kinds of breast cancer:

* Slow-growing tumours that would likely be found and treated without screening;

* Aggressive cancers that are deadly, whether they are detected by screening or not;

* Innocuous lesions or growths that are not deadly and frequently result in overdiagnosis and overtreatment;

* Potentially deadly tumours that are detected at just the right time by screening to allow for lifesaving treatment.

The latter group consists of about one in 1,000 women. Do those numbers justify the cost of screening, which is in the neighbourhood of $500-million annually?

Probably – but only if screening is done judiciously, targeting the women who will benefit most and are least likely to be harmed.

That is the 50-to-74 age group. And that is why the task force made its recommendation – not to save money; not because they hate women; not because they are oblivious to the scourge of breast cancer.

No, the recommendations are based on the latest science, not on wishful thinking. The evidence, no matter how displeasing or counterintuitive, must guide us.

And as Dr. Susan Love, the breast cancer pioneer (and supporter of screening over 50), is fond of reminding us: "All too often, when it comes to breast cancer, we seem to get caught up in wishful thinking and forget about science."