The prostate is located behind the pubic bones in a man’s pelvis, between the bladder and the rectum. When healthy, it is about the size of a walnut. A tube, called the urethra, runs through the middle of the prostate and drains urine from the bladder out of the penis. Two sex nerves for erection of the penis run next to and alongside the prostate. The purpose of the prostate is to produce seminal fluid, which when mixed with the sperm from the testicles, creates semen. Prostate cells also secrete proteins into the bloodstream, one of which is called Prostate Specific Antigen (PSA); this protein plays a key role in detecting cancer. See Figure 3 below.