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In 2009, The New York Times published a front-page bombshell: The American Cancer Society was about to reconsider its message about the risks and benefits of cancer screening. "I'm admitting that American medicine has overpromised when it comes to screening," said Dr. Otis Brawley, the society's chief medical officer. "The advantages to screening have been exaggerated."

The backlash was ferocious. Dr. Brawley was attacked by cancer doctors (especially radiologists) who insisted that reduced screening would cause unnecessary deaths. Women swore that early detection of breast cancer had saved their lives, and other women testified that if only they had been screened earlier, they might have avoided a death sentence. Cancer advocacy groups went on the warpath. Some people smelled a plot to ration health care, and legislation was introduced in the Senate to mandate access to mammography. The opposition was so fierce that the cancer society quickly backpedalled.

The whole drama was repeated in Canada this week, when an expert panel said that women in their 40s do not need routine screening with mammography. Once again, the cold science of statistics and the intense emotions of women and their families made for an explosive mix. Anxious women were left with the lame advice to consult their doctors and decide what's right for them.

The truth – as The Globe and Mail's André Picard so ably explained – is that Dr. Brawley was right. The value of mammography screening, especially for younger women, has been decisively disproven. Many experts go further and say that it's of no value, period. Recent declines in mortality from breast cancer, they argue, are entirely due to improved treatment, not to screening. In one Danish study, for example, women between 55 and 74 who had regular mammograms had a 1 per cent annual decrease in breast-cancer mortality. But women who were unscreened had a 2 per cent annual decrease.

Another analysis of six European countries that introduced breast cancer screening 10 to 15 years apart showed no relationship between the beginning of screening and breast-cancer mortality. In fact, all of the countries had similar breast-cancer mortality. As Danish cancer expert Peter Gotzche concluded, "If screening was a drug, it would have been withdrawn. You don't market a drug that harms so many people for such uncertain benefit."

There's nothing inherently wrong with the notion of screening for breast cancer. The problem is that the test is lousy. It picks up harmless cancers that never would have been a problem. Almost all the harmful cancers it picks up would have been detected anyway by other means. Instead of saving lives, screening creates an avalanche of overdiagnosis and needless treatment. And the benefit is vanishingly small: For example, 2,100 women in their 40s would have to be screened every two years for more than a decade to prevent a single breast-cancer death. Of those 2,100 women, 690 would have a false positive result, 75 would undergo unnecessary biopsies and others would have needless surgery. Another recent study found that more than half the women who have annual mammograms in their 40s will be called back for more testing because of false positives.

The same story is playing out with prostate cancer. Last month, the same U.S. scientific panel that recommended scaling back on mammograms said healthy men should no longer have PSA tests at all. The panel concluded flatly that the test doesn't save lives. But it does inflict devastating harm on men whose cancers would have otherwise been benign. The panel found that between 1986 and 2005, one million men were treated for prostate cancer because of the test. At least 5,000 died soon after surgery. As many as 70,000 suffered serious complications, and 200,000 to 300,000 suffered impotence, incontinence or both.

More and more expert groups have now come out against the PSA test. Among its leading critics is Richard Ablin, the man who discovered the prostate-specific antigen for which the test is named. He argues that the test is harmful and costs a fortune – the annual bill for PSA testing in the U.S. is at least $3-billion.

So why is it still used so widely? Partly because the medical establishment – including thousands of radiologists and urologists – has a big emotional, intellectual and financial investment in the PSA industry. Drug companies "continue peddling the tests and advocacy groups push 'prostate cancer awareness' by encouraging men to get screened," he wrote in an opinion piece published last year in the Times. "… I never dreamed that my discovery four decades ago would lead to such a profit-driven public-health disaster."

But it's not just the medical establishment that's so invested in these tests. We are, too. I have close friends of both sexes who swear that screening saved their lives. I also have a friend who was devastated by the news that she had Stage 0 breast cancer, which is often harmless if left alone, and another who nearly died of complications from prostate surgery.

We've been raised to be vigilant about our bodies – all our lives, warned of the risks that lurk within and without, and told that it's our duty to reduce them. We've all been told that we have far more control over our fate than we really do, and we believe it.

It's tragic to waste billions on medicine based on faith. But until we give up our illusions of control – and stop insisting on cures at any cost – we'll keep on doing it.