Prostate cancer is a tumor that grows in the prostate gland in men.
The prostate gland is part of the reproductive system. It stores seminal fluid, the substance that mixes with sperm to form semen. Normally, the prostate is a firm, walnut-shaped gland at the base of a man's bladder. It surrounds the urethra, the tube that carries urine from the bladder to the outside of the body. A man with prostate cancer has a tumor in the prostate gland.