Healthy Skepticism Library item: 9974

Warning: This library includes all items relevant to health product marketing that we are aware of regardless of quality. Often we do not agree with all or part of the contents.

Publication type: news

Priest A.
To Screen or Not to Screen
Shared Vision 2007 May 1
http://www.shared-vision.com/sv-health/20070501/to-screen-or-not-to-screen

Full text:

Do mammography and PSA tests do more harm than good?

If you could see your future and try to change it, would you? When it comes to cancer, apparently many would. As a society, we place enormous faith in screening tests designed to hunt out harbingers of disease in healthy people with no symptoms of sickness whatsoever.

This spring, the B.C. government gave $2 million to the Canadian Breast Cancer Foundation BC/Yukon to raise awareness of the benefits of mammography. The move was billed as breast-cancer prevention, even though screening doesn’t prevent disease; it’s just hoped that it will be caught early. In healthy men, the popular screening tool is PSA (prostate-specific antigen) tests for prostate cancer.

In theory, screening’s search-and-destroy strategy makes sense. Cancer is often a slow-growing, invasive disease, and if caught early, the thinking goes, it can be stopped in its tracks. If only it were so simple. But given the environment where screening occurs-a quagmire of biology, human nature, and a market-driven health-care system-it isn’t. In fact, mammography and PSA tests are fraught with controversy, complexity, and uncertainty.

That’s because the ultimate value of routine screening boils down to one question: “Does it save lives?” If the treatment or investigation for the disease works without causing harmful side effects, it probably does. But if the treatment/investigation causes harm, it probably doesn’t. Cancer is a complex disease; in fact, it is many different diseases with different outcomes. With breast cancer, some growths are best found early and removed. Some spread so quickly they have invaded the body years before they show up on a mammogram. Others grow so slowly that a woman would fare just as well if she found the lump herself. Many will never become invasive and never threaten a woman’s life. Right now, science is not good at telling the difference between cancers that will spread and those that will not.

The situation is similar with prostate cancer, a slow-growing disease that most sufferers die with, not of. According to the Mayo Clinic, even though about 17 per cent of men will be diagnosed with prostate cancer, only about three per cent will die of it.

Earlier this year, a study published in The Archives of Internal Medicine concluded that PSA testing does not save lives. Researchers said healthy men should be told of the potential risks of PSA screening, rather than simply urged to get tested.

Most people assume screening tests are valuable because they hear about only those who were truly diseased and benefited from early detection. Less publicized are those who are tested and told that they probably have cancer, when they don’t. Or those who are told they don’t have cancer, when they do.

The first, called a false positive, causes unnecessary anxiety, costs millions of dollars, and can lead to serious harm. Those given a false-positive result go on to have further investigation, such as more x-rays, surgery, or aggressive procedures, all of which carry risks. For instance, many men with elevated PSA choose to have surgical removal of the cancer, which can lead to impotence and incontinence. False negatives, on the other hand, are dangerous because they lead people to ignore symptoms they may have acted on.

False positive results are much more common than people think. Last fall, a review by the highly respected Cochrane Collaboration estimated that, for every 2,000 women who get mammograms for 10 years, one woman’s life will be prolonged, but another 10 healthy women will undergo unnecessary treatment. A further 200 will have the anxiety-inducing experience of being told about a suspicious finding that further testing reveals to be benign.

Mammography has been criticized ever since it began, more than 30 years ago. Last month, breast x-rays came under renewed fire when the American College of Physicians, the U.S.’s largest medical-specialty group, concluded that routine screening of women between 40 and 49 years of age probably causes more harm than good. (Canada does not recommend women begin routine mammograms before age 50.) The group did so after reviewing scientific evidence indicating that the breast cancer death rate in women 40 to 49 actually rises after screening begins.

Screening mammography and PSA testing are obviously double-edged swords. Although they may be of some value to those in high-risk groups, they no longer deserve the enormous amount of medical and financial resources we give them. Instead, attention needs to be paid on better ways of finding out which tumours require aggressive treatment and which don’t. And, most importantly, to finding out what elements in our degraded environment cause cancers. After all, more than half of all cancers are preventable.

Alicia Priest is a Victoria freelance journalist who chooses to spin the wheel and not have annual mammograms.