Can Aspirin Prevent Cancer?

By MICHAEL D. LEMONICK

Less than a decade ago, aspirin seemed to be losing some of its luster. Marketed since the beginning of the century as a uniquely effective pain and fever fighter, it was suddenly forced to compete with two major rivals -- acetaminophen (Tylenol, Anacin-3) and ibuprofen (Advil, Nuprin) -- that had many of aspirin's benefits without some of its side effects. Worse, aspirin had been linked to Reye's syndrome, a rare but sometimes deadly condition that can afflict children after a bout of flu or chickenpox. Doctors immediately ceased to recommend it for most youngsters, and liquid Tylenol replaced orange-flavored children's aspirin in the family medicine cabinet.

But the wonder drug has made a wondrous comeback. In recent years it has been shown to be a powerful inhibitor of heart attacks and strokes -- a virtue neither acetaminophen nor ibuprofen can match. And last week came preliminary evidence of another major benefit: aspirin reduces the risk of death from colon cancer, a disease that kills 50,000 Americans a year. A major study by the American Cancer Society, reported in the New England Journal of Medicine, found that people who took 16 aspirin tablets or more each month (or equivalent doses of related but lesser known anti-inflammatory drugs) cut their risk of dying from colon cancer as much as 50%. "It is a very strong and consistent finding," says Dr. Michael Thun, lead author of the report.

Still, many questions remain. Since study participants were not randomly assigned to take aspirin, it is possible that those who did were generally more health conscious than average and less likely to develop cancer in the first place. Or perhaps aspirin users had more internal bleeding than the others -- a common side effect of aspirin -- and therefore had their colon cancers detected early and cured readily. The study did not measure the actual ( incidence of colon cancer, just deaths resulting from it.

But the age-old pain-killer may very well have direct anticancer properties. Unlike acetaminophen, which acts only on the central nervous system, aspirin (chemical name: acetylsalicylic acid) has an extraordinarily broad range of effects. The reason is that it interferes with the production of a diverse class of substances known as prostaglandins, which are found in nearly every body tissue. (Ibuprofen does too, but in a much more limited way.)

Some prostaglandins promote inflammation, fever and pain by sensitizing nerves to other chemicals released from injured cells. Aspirin's most familiar benefits come from interfering with these noisome processes. However, prostaglandins are also responsible for stimulating the production of the stomach's protective lining of mucus, which explains why too much aspirin can cause gastric distress and bleeding. Aspirin's ability to prevent strokes and heart attacks stems from its disruption of a prostaglandin that promotes blood clotting. As for colon-cancer prevention, it is possible that aspirin inhibits substances that play a role in cell proliferation. At least one such prostaglandin has been identified in lab animals. If aspirin does have this effect, it might prove useful in reducing the risks of other cancers as well.

Aspirin's list of unexpected benefits may not end with cancer. There is at least some evidence that it may be useful in preventing gum disease, gallstones, cataracts, miscarriages and even in treating viral diseases. Researchers in several fields eagerly await the results of the Women's Health Study, an ambitious trial involving 40,000 women, half of whom will be randomly assigned to take low doses of aspirin every other day for at least five years. Originally designed to see if aspirin can prevent heart disease in women as it does in men, the study will also look at rates of colon cancer, migraines, stroke and gum disease.

Until the results are in, doctors are not recommending that anyone go out and gulp aspirin for good health. The drug can have unpleasant and even dangerous side effects, including ringing in the ears and blurred vision, as well as stomach bleeding. A more serious problem is hemorrhagic stroke, caused not by a clot blocking the brain's blood vessels but by vessels that rupture. Moreover, prostaglandins appear to work in opposing pairs. The ones that promote clot formation, for example, are countered by partners that do the opposite. Too much aspirin can therefore cause the very problems that lower doses relieve.

Even if follow-up studies show that aspirin really does protect against cancer, doctors warn that it will never be a substitute for exercise, a low- fat, high-fiber diet or not smoking. Too many heart-disease patients have latched on to aspirin as a panacea and as an excuse to avoid changing lethal habits. The latest findings will probably, alas, tempt others to do the same.

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CREDIT: TIME Graphic by Steve Hart

CAPTION: THE WONDER DRUG

With reporting by Andrew Purvis/New York