The prostate is the gland that produces semen (the fluid that carries sperm) and is essential for reproduction. About the size of a walnut, the prostate is located below the bladder and in front of the rectum. Cancer that begins in the prostate is called primary prostate cancer (or prostatic cancer). Prostate cancer may remain in the prostate gland or may spread to nearby lymph nodes. It could also spread to the bones, bladder, rectum and other organs.