Aflatoxins: data on human carcinogenic risk.

Some of the major difficulties in assessing the role of aflatoxin (AF) in the causation of liver cancer are discussed. Firstly, exposure to AF in Africa and parts of Asia and Latin America might begin very early in life and episodically thereafter. The number of episodes and the degree of exposure to AF varies greatly by country and region, by agricultural and crop storage practices, by season and by other factors difficult to control in any questionnaire-based study. Secondly, there is a high geographical correlation between exposure to AF and to hepatitis B virus. Thirdly, long-lasting biological markers for AF are still not available. Epidemiological studies might be enhanced by the incorporation of new biological assays. It is to be hoped that better information will be generated as a result of on-going intervention projects, such as reduction of AF levels and agricultural development programmes, and by monitoring exposure to AF and the incidence of liver cancer in areas where hepatitis B virus vaccination is effectively reducing the prevalence of carriers of the viral surface antigen.