1 Certain genetic disorders, such as Down syndrome, are associated with an increased risk of leukemia. 2  Exposure to certain chemicals. 3  Exposure to certain chemicals, such as benzene — which is found in gasoline and is used by the chemical industry — also is linked to an increased risk of some kinds of leukemia. 4  Smoking. Previous cancer treatment. 2  People who've had certain types of chemotherapy and radiation therapy for other cancers have an increased risk of developing certain types of leukemia. 3  Genetic disorders. 4  Genetic abnormalities seem to play a role in the development of leukemia.