Prevention: Is it just the right drug away?

Statins -- the cholesterol-lowering drugs that have shown benefits far outside their prescribed use -- are also under study in the prevention of a variety of cancers.

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A complex process

To be sure, agents that seem promising may later fall by the wayside. A combination of vitamin A and beta-carotene was one of the cancer chemoprevention community's most spectacular disappointments when, in studies completed in the 1990s, the regimen not only failed to reduce lung cancer rates but in fact boosted them among male smokers.

Still, many common nutrients -- including beta-carotene -- remain under investigation as potential cancer-blockers. Folic acid, vitamin D, selenium, lycopene, the spice ingredient curcumin, green tea and resveratrol, a compound found largely in the skins of red grapes, all are being tested in clinical trials.

The wide variety of chemicals that might help prevent cancer reflects the range of processes that go wrong when cells turn malignant. Dr. Michael Sporn, a professor of medicine and pharmacology at Dartmouth Medical School, says that different agents may disrupt the processes leading to cancer at different stages. It may prove that combinations of agents will be the most powerful, he says.

But if the search for cancer-preventing medicines is to bear fruit, he thinks that cancer researchers, clinicians and the government's drug-safety regulators will have to rethink their attitudes about risk, reward and medicine.

"The notion of preventing cancer is intuitively obvious to everyone but the oncology community," Sporn says.

In some ways, cancer-prevention drugs have the deck stacked against them, experts say. Most cancer chemotherapy drugs are known to come with horrific side effects. But the balance of risk and benefit often looks good anyway: Patients and their physicians usually calculate that likely side effects compare favorably with the far worse prospect of letting cancer run its course.

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Risk vs. benefit

In prevention, the calculation of risk and benefit is much more complex. What doctor would ask a patient whose future risk for cancer is uncertain -- and who by all appearances is currently well -- to take a cancer-prevention drug with recognized side effects such as liver toxicity or increased risk of stroke or heart attack?