Most prostate cancers are hormone-dependent and use the male hormone testosterone to grow. Hormonal therapy works by lowering the amount of testosterone available in the body to act on the prostate and thus it slows the cancer growth.  Hormonal therapy is given by medication, which decreases or blocks testosterone in the body or by removing the testicles (orchiectomy). Hormone therapy is usually given either to shrink the prostate or in cases where the cancer has spread beyond the confines of the prostate gland.