image by Ben Seidelman (lic)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, is 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. This cancer 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, most prostate cancers are caught early enough to be treated effectively. Thus the long term survival rate is very high.