The Globe and Mail

I have a new doctor. In her office is that poster – the one showing you how to do a breast self-examination every month. I’ve been looking at that poster since I was 12, and it always makes me feel guilty. Yet according to much of the evidence, BSE is about as effective at detecting breast cancer early as dowsing is at detecting water.

So why don’t they take it down? I think it’s because everyone believes that the best way to ward off cancer is eternal vigilance.

To make my doctor happy, I got a mammogram. I hadn’t had one in years, and she wondered why. Older women who don’t get regular mammograms are regarded as shockingly negligent about their health, or else kooky, like anti-vaccinationists. But now comes one more study (how many of them have there been?) that says the benefits of mammograms are marginal, at best.

The study was published this week in The New England Journal of Medicine. The lead author is Mette Kalager, a top Norwegian breast-cancer surgeon. The researchers thought that because mammography screening has improved so much, they would find that it’s even more effective than it used to be. They expected to find that regular mammograms reduce the death rate by a third.

Instead, they found the benefits are extremely modest.

Well, so what? Isn’t it worth it if you’re the one who dodges the bullet?

Maybe, maybe not. The Kalager study found that regular screening reduces the death rate from breast cancer by, at most, 10 per cent. That sounds enormous. But here’s what it means in the real world. Take 1,000 50-year-old women and track them for a decade. Without screening, 995.6 won’t die of breast cancer. With screening, 996 won’t die. The difference over a decade amounts to 0.4 per thousand women.

Let me numb you with more statistics. Take 2,500 women who are 50 years of age, and screen them for the next 10 years. Up to 1,000 of them will have at least one “false alarm,” and about half of those will undergo biopsy. Breast cancer will be over-diagnosed in five to 15 women, who will be needlessly treated with surgery, radiation, chemotherapy, or a combination. Many of these women will swear a mammogram saved their lives, even though all it did was subject them to painful, useless slashing and burning. One woman will avoid dying from breast cancer.

In fact, because of increased awareness and big improvements in treatment, the real reduction in the death rate may be more like 2 per cent – an amount so small, writes Dr. Gilbert Welch in the same issue of the NEJM, that it’s barely meaningful.

No screening test has been more carefully studied than mammography. And the Kalager study is just the latest one to confirm that the benefits of screening are negligible. Yet screening mammography has become one of the leading measures of health-care performance. “The public widely perceives screening mammography to be one of the most important services provided by modern medicine,” Dr. Gilbert writes. “The perception is largely the product of well-crafted public-health messaging.” His advice to cancer agencies: Dial it back. His advice to women like me is: Get screened if it makes you feel better – but be aware of the downside.

The news on prostate-cancer testing is even less equivocal. Mass screening appears to deliver no benefits at all. It may even do more harm than good, especially in the U.S., where screening is more common than in Canada and treatment more aggressive. Blood tests for PSA levels are a crude cancer marker in the first place. Biopsies often discover cancers that aren’t dangerous, but are surgically treated anyway. The long-term aftereffects of surgery can be extremely disagreeable and permanent.

Even Otis Brawley, chief medical officer of the American Cancer Society, is a skeptic. “American medicine has over-promised when it comes to screening,” he said last year. He doubts that PSA testing saves more lives than it ruins. His semi-unofficial advice to guys: You really don’t want to go there, and you’ll probably be better off if you don’t.

Despite the mounting evidence, many, many doctors, radiologists and biostatisticians continue to believe it’s better to be safe than sorry. After all, they’ve invested their whole careers in the benefits of early detection through screening. To admit that screening isn’t useful goes against their every instinct – and the public’s, too.

For years, we’ve been urged to take control and be proactive about our health. When something looks alarming – especially when that something is diagnosed as cancer – we want to cut it out as soon as possible. Many of my friends of both sexes, after learning that a potential cancer lurks within, have been stricken with anxiety so crippling they can barely function.

We’ve been encouraged to control our destinies, and to a large extent, we do. We have immense faith in the experts and their advanced technologies. We believe in expertise. We’re wealthy. And we believe that so long as we deploy that expertise and wealth, we will be able to improve the outcomes in our favour. That’s often true. But the idea that sometimes we might be just as well off to sit back – and do nothing – is anathema to every fibre of our being.

Yet even Dr. Kalager, the breast-cancer surgeon, has changed her mind about the benefits of screening. As she told The New York Times, she worries about the small chance of benefit compared to the large chance of finding and treating a cancer that didn’t need to be treated. Every woman’s decision about screening should be respected. But at the same time, she cautions, “Since I’m a breast cancer surgeon, I know what being treated is like.”