This cancer forms in tissues of the prostate (a gland in the male reproductive system found below the bladder and in front of the rectum). The prostate surrounds the urethra, the tube through which urine flows. A healthy prostate is about the size of a walnut. If the prostate grows too large, it squeezes the urethra. This may slow or stop the normal flow of urine. Prostate cancer usually occurs in older men.
SEER Cancer Stat Facts: Prostate Cancer. National Cancer Institute. Bethesda, MD, http://seer.cancer.gov/statfacts/html/prost.html