Chemotherapy is the use of strong drugs to kill cancer cells. It is not a common treatment for prostate cancer, but it may be used if cancer has spread outside the prostate gland and hormone therapy has been unsuccessful. Typically, chemotherapy drugs for prostate cancer are usually given intravenously (injected into a vein). Doctors give chemotherapy in cycles, with each period of treatment followed by a rest period to allow the body time to recover. Each cycle typically lasts for a few weeks.