UNLESS NATIONAL HEALTH WILL RATION BASED ON SUCH EVIDENCE, IT'S USELESS:

Medicines to Deter Some Cancers Are Not Taken (GINA KOLATA, 11/13/09, NY Times)

[I]t turns out, there is a way to prevent many cases of prostate cancer. A large and rigorous study found that a generic drug, finasteride, costing about $2 a day, could prevent as many as 50,000 cases each year. Another study found that finasteride’s close cousin, dutasteride, about $3.50 a day, has the same effect.

Nevertheless, researchers say, the drugs that work are largely ignored. And supplements that have been shown to be not just ineffective but possibly harmful are taken by men hoping to protect themselves from prostate cancer. [...]

A few ways are known for sure to prevent cancer; the biggest is to avoid cigarette smoking. That alone would drop the cancer death rate by a third. No other measure comes close.

Another huge success, for breast cancer, is to avoid taking estrogen and progestin at menopause. Sales of those drugs plummeted in 2002 after a federal study, the Women’s Health Initiative, concluded that they did not prevent heart disease and might increase breast cancer. The next year, the breast cancer rate dropped by 15 percent after having steadily increased since 1945.

The vaccine for human papilloma virus, protects against most strains of the virus, which causes cervical cancer.

But other measures that are often assumed — and marketed — as ways to prevent cancer may not make much difference, researchers say.

For example, public health experts for years recommended eating five servings of fruits and vegetables a day to prevent cancer, but the evidence is conflicting, at best suggestive, and far from definitive.

Low-fat diets were long thought to prevent breast cancer. But a large federal study randomizing women to a low-fat or normal diet and looking for an effect in breast cancer found nothing, said its director, Ross L. Prentice of the Fred Hutchinson Cancer Research Center in Seattle.

Fiber, found in fruits, vegetables and grains, is often thought to prevent colon cancer, even though two large studies found no effect.

“We thought we would show relationships that were strong and true,” said Dr. Tim Byers, professor of epidemiology at the Colorado School of Public Health, “particularly for dietary choices and food and vegetable intake. Now we have settled into thinking they are important but it’s not like saying you can cut your risk in half or three-quarters.” Others wonder whether even such qualified support is misplaced.

There has to be a reason the research disappointed, said Colin B. Begg, chairman of the department of epidemiology and biostatistics at Memorial Sloan-Kettering Cancer Center. Perhaps the crucial time to intervene is early in life.

“That’s one possibility,” Dr. Begg said. “The other is that it’s all sort of nonsense to begin with.” [...]

Dr. Peter Greenwald knows the dashed hopes of cancer prevention research firsthand. As far back as 1981, when he arrived at the National Cancer Institute to direct “cancer prevention and control,” Dr. Greenwald began thinking about testing whether simple measures, like vitamin supplements, could prevent common cancers.

He focused on what looked like it could be a sure thing — beta carotene, found in orange fruits and vegetables as well as in green leafy vegetables.

The body converts beta carotene to vitamin A, which can prevent cancer in rats. People eating the most fruits and vegetables had less cancer. And the more beta carotene in a person’s blood, the lower the cancer risk. Lung cancer seemed particularly vulnerable to beta carotene’s effects, particularly in smokers and former smokers.

What was needed was cause-and-effect evidence, studies showing that if people bolstered their beta carotene and vitamin A levels, they would be protected from cancer. The cancer institute decided to take it on with two large studies.

But not only did the supplements not work, but there was evidence that beta carotene might actually increase cancer risk in smokers.