The prostate is a gland that exists in men only, as a part of their reproductive system. Its primary purpose is to manufacture the liquid part of semen (male reproductive fluid); the actual active ingredient in semen, the sperm, are produced in the testicles. The prostate also helps to control urination based on its placement surrounding the urethra. Prostate cancer occurs when a malignant (cancerous) tumor starts to grow inside the prostate.
Prostate cancer is relatively common, with some 230,000 American men diagnosed each year. It can lead to conditions such as impotence (inability to have an erection) and loss of bladder control, and in a minority of cases it can be lethal. Luckily, about 85% of prostate cancer cases are diagnosed early enough during the disease progression that they can be effectively treated. The long term survival rate is very high.