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Every woman knows the breast cancer catechism by heart. Early detection is crucial, and prevention measures are important. Regular mammograms are essential - probably the more the better. For years, we've been lectured on the importance of breast self-examination, and every gym had waterproof instructions posted in the showers. We knew the lifestyle advice: Eat your fruits and veggies, get lots of exercise, don't drink too much, don't get fat.

But now we're learning that much of this advice is about as useful as lucky charms to ward off the evil eye.

In the U.S., a leading advisory panel on breast cancer touched off a storm of controversy this week when it recommended against routine mammograms for women in their 40s. Experts filled the airwaves. Some endorsed the new guidelines, some did not, and some said women should consult their doctors. Others issued dire warnings: "Women are the first group to suffer when cost cutting takes precedent over sound medical care," said one female doctor.

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The new U.S. guidelines look a lot like Canada's. They say screening isn't useful for women in their 40s and that, after 50, every other year is good enough. As for breast self-exams, they do no good at all.

For a generation of women who've learned to be super-vigilant about breast cancer, the news came as a shock. How can less screening be better? So here's a bigger shock: Screening can do more harm than good.

"A lot of [women]have not been fully informed about the over-diagnosis scenario," says Cornelia Baines, who led a landmark study of mammography in Canada. Mammography is not a very good tool. It detects many cancers that would be harmless if left untreated (and sometimes misses deadly ones). And a horde of people must be screened to avoid one death. If 2,000 women are screened regularly for 10 years, only one will avoid death from breast cancer. But 10 healthy women will undergo unnecessary treatment because of false positives.





Over-diagnosis has plenty of social and personal side effects - needless surgery and trauma, emotional anguish, wasted money and resources. Last month, The New York Times reported that the American Cancer Society is changing its message about screening for breast cancer. "The advantages to screening have been exaggerated," said Otis Brawley, the cancer society's chief medical officer. Its new message will emphasize the risks as well as the benefits.

The emphasis on early detection has made the problem worse. "With the advent of widespread efforts to diagnose cancer earlier, over-diagnosis has become an increasingly vexing problem," writes U.S. cancer expert Gilbert Welch. How big is the problem? One gold-plated research study, conducted by the Nordic Cochrane Centre group, says that as many as one in three women are treated unnecessarily. The problem, of course, is that we don't know which ones.

The over-diagnosis problem is well known in medical circles. But cancer agencies have been slow to acknowledge it, because it's hugely political. "If you question over-diagnosis in breast cancer, you are against women," cancer expert Peter Albertson told The New York Times. It is also political because large segments of the medical industry - including radiologists, surgeons, pathologists and medical-equipment vendors - stand to lose if screening is cut back.

The idea that screening carries risks undermines the main cancer narrative of our age - that it is under-detected, under-treated and invariably lethal. The prevention narrative is wrong, too. With the obvious exception of lung cancer, it turns out there's not much you can do to prevent cancer. Despite extensive research, no clear link has yet been found between breast cancer, diet and exercise.

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So why do we want so hard to believe? "It's wishful thinking," says cancer expert Susan Love. "We would like things to be more in our control."

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