context: Prostate cancer is a complex disease. Doctors cannot always predict how fast or slow it will grow. Nor do they agree on when to treat it, or which treatments to use. Predicting and monitoring the disease with accuracy help doctors and patients make decisions that result in the best survival rates and quality of life. If you are diagnosed with prostate cancer, your doctor will probably evaluate several factors to determine how aggressive it is. These "markers" identify whether the cancer is low risk, intermediate risk, or high risk. Low-risk prostate cancer is slow growing and not likely to spread quickly. High-risk prostate cancer is aggressive, meaning it is likely to spread quickly outside the prostate. Understanding the risk level of your cancer will help your doctor decide on the treatment that's right for you. Your doctor will look at key "markers" for aggressive cancer, as well as the "stage" of your specific cancer. Commonly used markers for prostate cancer include: Prostate-specific antigen ( PSA) levels. PSA is a substance produced by the prostate gland. It is normal to secrete small amounts of PSA into the bloodstream. Larger amounts of PSA in the bloodstream usually signal that the prostate gland is enlarged, infected, or malignant. PSA levels are determined by a simple blood test. The higher the number, the more likely the patient is to have prostate cancer. PSA velocity. Several studies indicate that when PSA levels increase sharply in the months before surgery, the cancer is likely to be aggressive. Gleason score. The cells in the tumor are graded on the basis of how abnormal, or normal they look when the tissue is examined under a microscope. The tumor is given a grade, from 1-5. The two most common abnormal areas are evaluated. These numbers are then added. This number is called the Gleason score. The higher the number, the more aggressive the tumor and the more likely its spread. A tumor with a Gleason score of 6 or lower is less likely to spread. The stages of prostate cancer refer to the cancer size and how far it has spread. The stages are: Localized Prostate Cancer is stage I to stage IIIA. At this stage, the tumor is confined to the prostate. Regional Prostate Cancer, also known as local extension, is stage IIIB to IVA. The tumor has grown through the prostate capsule, either into the seminal vesicles (a pair of glands next to the prostate) or into nearby muscles and organs. Metastatic Prostate Cancer is referred to as stage IVB. The tumor has spread to the distant lymph nodes or more distant parts of the body. Attention to the general health of a patient as well as the patient's wishes are also an important part of treatment decisions. If you are diagnosed with prostate cancer, your doctor will monitor the disease periodically to see if it is spreading and how well treatments are working. PSA continues to be the primary marker of how the disease is progressing or responding to treatment. Several recent studies indicate that PSA doubling time -- the time it takes for a patient's PSA level to double -- predicts how aggressive the cancer is. The faster the PSA level doubles, the more aggressive the cancer. When prostate cancer spreads, it usually goes to the bones or lymph nodes. Imaging techniques are available to see whether the cancer has spread to the bones and, if so, to what extent. Imaging techniques currently used include: Bone scans create images of bones on a computer screen or film. The patient is injected with a small amount of radioactive material that travels through the bloodstream. The computer screen detects radioactive material that has collected in abnormal areas of the bone. CT scans make computerized X-ray images that produce cross-sectional images of the body. These detailed images can reveal disease or abnormalities in tissue and bone. Researchers are seeking more accurate ways of diagnosing, monitoring, and treating prostate cancer. Many of the studies focus on genes and genetic abnormalities of a cancer. Scientists have found that the product of a certain gene appears more often in advanced prostate cancers than in early stage prostate cancers. Now the goal is to determine if the presence of this gene product means that a cancer is more aggressive. Knowing this information can help doctors decide which patients may benefit from immediate treatment, and of what type. This and other genetic research will pave the way for earlier, more accurate predictors of cancer growth.