Cancer is a group of abnormal cells that grow more rapidly than normal cells and that refuse to die. Cancer cells also have the ability to invade and destroy normal tissues, either by growing directly into surrounding structures or after traveling to another part of your body through your bloodstream or lymph nodes. Microscopic cancer cells grow into small clusters that continue to grow, becoming more densely packed and hard.

Prostate cancer usually grows slowly and remains confined to the prostate gland, where it usually doesn't cause serious harm. But not all cancers act the same. Some forms of prostate cancer are aggressive and can spread quickly to other parts of your body.

What causes prostate cancer and why some types behave differently are unknown. Research suggests that a combination of factors may play a role, including heredity, ethnicity, hormones, diet and the environment.

Knowing the risk factors for prostate cancer can help you determine if and when you want to begin prostate cancer screening. The main risk factors include:

• Age. As you get older, your risk of prostate cancer increases. After age 50, your chance of having prostate cancer increases substantially.

• Race or ethnicity. For reasons that aren't well understood, African-American men are more likely to get and die of prostate cancer than are men of any other group. Black men are twice as likely to die of prostate cancer. 

• Family history. If a close family member — your father or brother — has prostate cancer, your risk of the disease is greater than that of the average American man.

• Diet. A high-fat diet and obesity may increase your risk of prostate cancer. Researchers theorize that fat increases production of the hormone testosterone, which may promote the development of prostate cancer cells.

• Surgery to become infertile (vasectomy). Although some studies suggest that men who've had a vasectomy are at increased risk for prostate cancer, no conclusive evidence to support such research has been found. Research on this issue remains in progress.