Exposure to the chemical benzene or high doses of radiation increases the risk of leukemia. Environmental exposures to radiation are generally at a low dose and may increase your risk of developing leukemia. High dose radiation is something usually only cancer patients are exposed to, and this exposure is necessary to cure a present cancer. The risk of the cancer coming back without radiation therapy is far greater than the risk of developing leukemia from the radiation, and you should not avoid radiation because of this small leukemia risk. There are certain types of chemotherapy drugs that can also increase your risk of leukemia, such as melphalan, mechlorethamine, and other drugs called alkylating agents.