Diet, Drugs May Stop Prostate Cancer

Trials Poised to Identify Prevention Strategies

Medically Reviewed by Louise Chang, MD on September 24, 2007

Sept. 24, 2007 -- How to lower cancer risk in men is one of the hottest areas in prevention research. Now a new study shows there should be some definitive answers on prostate cancer within the next few years.

A host of trials are under way investigating drug treatments, nutritional supplements, and foods that have shown promise for the prevention of prostate cancer.

Urologist and prostate cancer researcher Neil Fleshner, MD, MPH, of the University of Toronto, says these trials should soon lead to effective evidence-based strategies to prevent the disease.

Fleshner’s review of the prostate cancer prevention research appears in the latest online issue of the journal Cancer.

“There is great hope that within the next five years we will have relatively inexpensive and very effective ways to minimize the burden of prostate cancer,” he tells WebMD.

But a cancer epidemiologist who also spoke to WebMD called the five-year timeline optimistic.

“Results from these clinical trials should shed some light on what can be done, but I am doubtful that they will provide all the answers,” says Carmen Rodriguez, MD, of the American Cancer Society.

Food, Drug Strategies for Prevention

Several studies have linked the consumption of animal fat -- especially fat found in red meat and high-fat dairy products -- to an increase in prostate cancer risk.

The overall health benefits of limiting red meat and high-fat dairy foods are well-known. Fleshner says reducing prostate cancer risk may prove to be one more benefit of eating a diet high in fruits and vegetables and low in animal fat.

One of the most promising strategies for preventing prostate cancer in high-risk men had been treatment with the prostate enlargement drug finasteride (known commercially as Proscar) or similar drugs.

But a large trial of finasteride, involving close to 19,000 men who were at average risk for developing the disease, produced confusing results.

While the men in the Prostate Cancer Prevention Trial (PCPT) who took the drug had a 25% reduction in prostate cancers compared with men who didn't, they also had more advanced and aggressive tumors.

The clinical significance of both of these findings remains in doubt. It is not clear if finasteride actually promotes higher-grade tumors or if the finding was due to the study design.

But the bigger reason why the drug is not used more for prostate cancer prevention is doubt about whether it prevents cancers that lead to death, Fleshner says.

“Most doctors still have questions about whether the types of tumors prevented with finasteride are actually clinically relevant,” he says.

It is also not clear if potential side effects, such as impotence and decreased sex drive, will keep men from taking the drug for prostate cancer prevention or just who should take it if it proves beneficial, Rodriguez says.

A large clinical trial of a similar drug, Avodart, is ongoing. The trial involves more than 8,000 men at high risk for developing prostate cancer, and results are expected within the next few years.

Another approach to chemoprevention involves treatment with the antiestrogen breast cancer drug Fareston.

Early trials found that men treated with low doses of the drug (20 milligrams) developed slightly fewer prostate cancers than those treated with placebo or higher doses of Fareston. Results from a definitive study should be reported within the next two years, Fleshner says.

Vitamin E, Selenium, and Soy

A large, National Cancer Institute-run trial is under way assessing the role of vitamin E and the nutrient selenium in prostate cancer prevention. The research was spurred by smaller studies suggesting a protective benefit for the supplements.

Roughly 35,000 men have been recruited for the study, which will compare outcomes among men taking either 400 International units (IU) of vitamin E, 200 micrograms of selenium, a combination of the two supplements, or a placebo each day.

Enthusiasm about the use of vitamin E for disease prevention has been tempered by recent studies suggesting that doses higher than 400 IU a day may be associated with an increased risk of death.

Fleshner says he recommends 200 IU of vitamin E daily along with selenium to many of his patients who want to do something to lower their risk.

“On one hand I am conflicted, because we don’t have the definitive data,” he says. “But I have a history of prostate cancer in my family, and I take these agents myself, so I am not telling patients to do anything that I am not doing.”

Nutritional interventions such as soy, green tea, and the antioxidant lycopene, found primarily in tomato-based products, are also being studied for prostate cancer prevention.

Very early investigations suggest a preventive role for diabetes drugs like metformin and the cholesterol-lowering statin drugs.

Rodriguez says some of these strategies may prove effective for reducing prostate cancer risk. But she adds that many relevant questions are likely to remain unanswered for years to come.

“A big issue is that we are really not able to differentiate early cancers that may become clinically relevant from those that will not,” she says, adding that until this is possible it will be difficult to interpret results from prostate cancer prevention trials.

Show Sources

SOURCES: Fleshner, N. Cancer, Nov. 1, 2007; vol 110: online edition. Neil Fleshner, MD, MPH, division of urology, University Health Network and Department of Surgery, University of Toronto, Toronto, Canada. Carmen Rodriguez, MD, epidemiologist, American Cancer Society, Atlanta.

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