If hormone therapy stops working, your doctor may suggest immunotherapy. It uses the immune system -- your body's defense against germs -- to attack the cancer cells. Specifically, sipuleucel-T (Provenge) is used to treat advanced prostate cancer. To make it, the doctor removes white blood cells from your blood. These go to a lab, where experts genetically engineer them to fight your prostate cancer. You then get these cancer-killing cells by IV injection in three separate treatments.