Except for skin cancer, cancer of the prostate is the most common malignancy in American men. In the majority of men with prostate cancer, it is very slow growing, and many, if not most, of these men will not die because of the prostate cancer, but rather will live with it until they eventually die of some other cause. Early prostate cancer is localized (confined) to the gland, and the majority of patients with localized prostate cancer have a long survival after diagnosis. All men are at risk in industrialized nations. The most common risk factor is age. 90% of men diagnosed with prostate cancer each year are over the age of 65. African American men have a higher risk of prostate cancer than white Americans. Dramatic differences in the incidence of prostate cancer are seen in different countries, and there is some evidence that a diet higher in animal fat may, in part, underlie these differences in risk. Genetic factors also appear to play a role, particularly for families in whom the diagnosis is made in men under 60 years of age. The risk of prostate cancer rises with the number of close relatives who have the disease.

Prostate cancer often does not cause symptoms for many years. By the time symptoms occur, the disease may have spread beyond the prostate.

Two tests are commonly used to detect prostate cancer in the absence of any symptoms. One is the digital rectal exam, in which a doctor feels the prostate through the rectum to find hard or lumpy areas. The other is a blood test used to detect a substance made by the prostate called prostate specific antigen (PSA). Together, these tests can detect many silent prostate cancers, those that have not caused symptoms.

Neither of the screening tests for prostate cancer is perfect. Most men with mildly elevated PSA do not have prostate cancer, and many men with prostate cancer have normal levels of PSA. Testing for the percentage of free PSA can help. The digital rectal exam can miss many prostate cancers.

In a 2003 study from the Memorial Sloan-Kettering Cancer Center in New York City, researchers collected five blood samples each from nearly 1,000 men whose median age was 62 years. More than 20% of the subjects were found to have PSA levels high enough that many doctors would have recommended a biopsy. Half of those men, however, had follow-up tests with normal PSA levels. The Sloan-Kettering team concluded that an isolated PSA screening with an elevated level should be followed with an additional screening several weeks later before proceeding with further testing or a biopsy.

Garzotto and his colleagues studied more than 1,200 men with PSA levels ranging from 4 to 10 (0 to 3 is considered normal) who had biopsies from 1993 to 2000. They found that the most important predictors of cancer were:

• A digital rectal exam to feel for a hardened nodule that may be a tumor.
• A transrectal ultrasound to look for a darkened area that may be cancerous.
• A man's age: 90% of prostate cancer cases are in men over 65.
• PSA density, which is the ratio between PSA level and prostate size. A smaller gland with elevated PSA is more likely to be cancer than a larger gland with elevated PSA.

When patients were given points on these criteria using a mathematical model called a nomogram, researchers could predict which men had the lowest odds of having cancer, potentially avoiding many unnecessary prostate biopies. [Garzotto, Online edition of Cancer, 8/25/2003]

However, the diagnosis of prostate cancer can be confirmed only by a microscopic examination to identify cancerous prostate tissue. This is done by a biopsy performed in the doctor's office.