Prostate cancer is the most common cancer diagnosed among American men, and causes more deaths annually among men than any other tumor except lung cancer. However, only a small proportion of prostate cancers diagnosed are ultimately lethal. A large majority of men found to have prostate cancer ultimately die of other causes, most commonly cardiovascular disease. All available treatments for prostate cancer (surgery, radiation therapy, hormonal therapy, and others) carry a risk of complications, side effects, and other impacts to the patient's long-term quality of life. Before making a decision regarding treatment for prostate cancer it is important to estimate the likelihood that a given tumor will recur after treatment, progress, and pose a threat to life.