Because the exact cause of prostate cancer is not known, at this time it is not possible to prevent most cases of the disease. Many risk factors such as age, race, and family history cannot be controlled. But based on what we do know, some cases might be prevented.

Diet

You may be able to reduce your risk of prostate cancer by changing the way you eat, but the results of research studies are not yet clear.

The American Cancer Society recommends choosing foods and beverages in amounts that help achieve and maintain a healthy weight, eating a variety of healthful foods with an emphasis on plant sources, and limiting your intake of red meats, especially high-fat or processed meats. Eat 5 or more servings of fruits and vegetables each day. Whole-grain breads, cereals, rice, pasta, and beans are also recommended. These guidelines on nutrition may also lower the risk for some other types of cancer, as well as other health problems.

Tomatoes (raw, cooked, or in tomato products such as sauces or ketchup), pink grapefruit, and watermelon are rich in lycopenes. These vitamin-like substances are antioxidants that help prevent damage to DNA. Some earlier studies suggested lycopenes may help lower prostate cancer risk, although a more recent study found no link between blood levels of lycopene and risk of prostate cancer. Research in this area continues.

Taking vitamin or mineral supplements may affect your prostate cancer risk, but this is not yet clear. Some studies suggest that taking 50 milligrams (or 400 International Units) of vitamin E daily can lower risk. But other studies have found that vitamin E supplements have no impact on cancer risk, and larger doses may increase risk for some kinds of heart diseases. Selenium, a mineral, may also lower risk. On the other hand, beta-carotene supplements may actually raise prostate cancer risk. Taking any supplements can have risks and benefits. Before starting vitamins or other supplements, you should talk with your doctor.

The possible effects of selenium and vitamin E on prostate cancer risk are now being studied in the Selenium and Vitamin E Cancer Prevention Trial (SELECT). This large clinical trial is under way, but the results will probably not be available for several years.

Several studies are now looking at the possible effects of soy proteins (called isoflavones) on prostate cancer risk. The results of these studies are not yet available.

Medicines

Some drugs may also help reduce the risk of prostate cancer.

5 alpha-reductase inhibitors

5 alpha-reductase is the enzyme that changes testosterone into dihydrotestosterone (DHT). DHT is the hormone which causes the prostate to grow. 5 alpha-reductase inhibitors are drugs that block that enzyme and prevent the formation of DHT.

Finasteride (Proscar) is a 5 alpha-reductase inhibitor that is already used to treat benign prostatic hyperplasia (BPH). It is also available in a lower dose form (called Propecia) to treat male pattern baldness.

The Prostate Cancer Prevention Trial (PCPT) was a large clinical trial designed to see if finasteride could lower the risk of prostate cancer. Half of the men in the study took finasteride each day for 7 years, while the other half took a placebo (sugar pill). At the end of the study, men taking finasteride were less likely to have prostate cancer than those getting the placebo. At first it looked like the men taking finasteride had slightly more cancers with high Gleason scores -- cancers that looked like they were more likely to grow and spread. It is now thought that this is not true and men who took finasteride are not more likely to develop high-grade cancer. Researchers are still watching the men in the study to see if the men taking the drug lived longer. (More information about the Gleason score can be found in the section, "How is prostate cancer diagnosed?")

Finasteride was more likely to cause sexual side effects such as lowered sexual desire and impotence. But it seemed to help with urinary problems such as trouble urinating and leaking urine (incontinence).

At this time, not all doctors agree whether taking finasteride to prevent prostate cancer is a good thing. Men thinking about this should discuss it with their doctors. The results of the PCPT will become clearer over the next few years.

Dutasteride (Avodart), another 5 alpha-reductase inhibitor, is currently being tested in a clinical trial to see if it can lower the risk of prostate cancer.

Other drugs

In a small study, toremifene, an anti-estrogen, decreased the risk of prostate cancer in men with high grade prostatic intraepithelial neoplasia. A larger study to confirm this finding is going on now. Other drugs that may help prevent prostate cancer are now being tested in clinical trials.