Drugs +/- radiation. Various chemotherapy drugs and new targeted therapies are used that preferentially kill cancer cells while minimizing side effects. Sometimes radiation is used alone or in addition to drugs depending on the type and stage of cancer. This is a discussion you will have with your cancer team during which you should have ample opportunity to ask questions. Take a pad and paper with you.
Mainly by drugs. The treatment of leukemia ranges from simple oral drugs (e.g. Chronic myeloid leukemia) to intensive chemotherapy (in most acute leukemias) and all the way to bone marrow transplantation (for high risk and relapsed leukemias). Radiation can be used to treat certain high-risk relapse areas like the spine or brain in certain situations.