Cancer is a group of many different diseases affecting the body’s cells. Normally, cells grow and divide only when the body needs them. If production continues when new cells are not required, excess tissue can form a mass, called a tumor. This tissue may be benign – which is not cancerous – or malignant, which is. When a malignancy occurs, cancer cells divide out of control, possibly invading and destroying nearby healthy tissue. Cancer cells also can break away from the tumor to enter the bloodstream and lymphatic system. This is how cancer spreads – or metastasizes – to form new tumors in other parts of the body.

The prostate is a male sex gland that produces fluid for semen. It is about the size of a walnut, located just below the bladder and in front of the rectum. The prostate surrounds the upper part of the urethra, which is the tube that empties urine from the bladder.

Prostate cancer occurs when malignant cells form in the gland. Cancer that remains confined within the gland is considered localized. If the disease spreads outside the prostate, it most often moves into surrounding tissues or the seminal vesicles (sac-like structures attached to the prostate). Further metastasis could involve the lymph nodes and, eventually, other organs.

Most prostate cancers grow very slowly. Autopsies indicate many elderly men who died of other causes also had undetected prostate cancer. However, because some forms of this disease can grow and spread quickly to other areas of the body, prostate cancer can be life threatening.