Chemically induced leukemia in humans.

The human population may be exposed to potentially leukemogenic agents, either in the form of drugs and food additives or as environmental contaminants and pollutants. However, in spite of the large number and diversity of these chemicals, only a few have been implicated as human leukemogens. One such agent is benzene, a known bone marrow depressant. A number of case reports have associated chronic exposure to this agent with the development of acute leukemia, as have several epidemiologic surveys. Treatment with various antitumor agents, including procarbazine, melphalan, thio-TEPA, chlorambucil, and cyclophosphamide, has also been associated with the development of acute leukemia. In addition, chloramphenicol and phenylbutazone have been implicated as human leukemogens, but the association between exposure to these two agents and acute leukemia appears at present to be weaker than it is for benzene and antitumor agent exposure. Despite such associations between exposure to chemicals and acute leukemia, several important problems exist with regard to implicating specific agents in the development of this neoplasm in man, including the paucity of animal models for chemically induced leukemia, and the frequent necessity to rely on single case reports or clusters of cases in which chemical exposures are associated with acute leukemia. Future efforts should be directed at performing properly designed and well executed epidemiologic studies, and at developing new in vitro and in vivo models for the study of this neoplasm.