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The prostate is a chestnut-shaped gland of the male reproductive system. It is about the size of a walnut that is located in front of the rectum and just below the bladder, and surrounds the beginning of the urethra (the tube that carries urine and semen out of the body). The prostate gland is somewhat conical in shape, and consists of a base, an apex, an anterior, a posterior and two lateral surfaces. The capsule is the fibromuscular membrane covering the prostate and is the anatomical boundary for The prostate is divided into several lobes:

• The anterior lobe is used to describe the anterior portion of the gland lying in front of the urethra.
• The median lobe is a cone-shaped portion of the gland situated between the two ejaculatory ducts and the urethra.
• The lateral lobes (right and left lobes) form the main mass of the gland. They are separated by the prostatic urethra.
• The posterior lobe describes the part of the lateral lobes that can be felt through the rectum during digital rectal exam (DRE).

The prostate is also described in terms of its three zones: the peripheral, the central, and the transitional zones. Of cases of prostate cancer, 70% arise in the peripheral zone, 15-20% arise in the central zone, and 10-15% arise in the transitional zone. Most prostate cancers are multifocal, with synchronous involvement of multiple zones of the prostate.

The main purpose of the prostate is to produce fluid for semen, which transports sperm during the male orgasm and to protect the bladder against bacterial invasion. The nerves involved in penile erection are located posteriorly on each side of the prostate gland. Therefore, the prostate is also considered to be an accessory sex organ.

The prostate normally increases in size around the age of puberty and then usually remains constant until the age of 45 to 50 years, at which time it may begin to undergo varying degrees of enlargement stimulated by rising levels of the male hormone testosterone. This non-cancer-related process is called benign prostatic hyperplasia (BPH) and can cause urinary problems in older men. Approximately 33% of men over the age of 50 have BPH.

The prostate can also develop cancer. Carcinoma of the prostate is the most commonly diagnosed male malignancy in the U.S. Because it grows so slowly, it often produces no symptoms and men often die of other causes before the cancer becomes an issue. Early detection is the key to successful treatment with a 5-year survival rate of greater than 80%.

In general, prostate cancers grow very slowly. It is known that the growth rate of prostate cancers increases in response to the presence of androgens (male hormones). Therefore, several treatments are targeted at reducing or eliminating androgens in the body.

In its advanced stages, prostate cancer can spread (metastasize) to other parts of the body including the lymph nodes, bone, spine, liver, lungs, adrenal glands and the brain.