The development of hepatocellular cancer in humans.

The biological characteristics of hepatocellular cancer vary appreciably in different parts of the world, but especially between regions with very high and low incidences of the tumour. Hepatocellular cancer is multifactorial in origin, and the pattern of its aetiological associations differs between populations at high and low risk. In Africans and Chinese, who have the highest incidences of hepatocellular cancer, the hepatitis B virus is the most important causal association. The viral carrier state is acquired during early childhood, and carries a relative risk for the development of the tumour of over 200. Integration of hepatitis B virus DNA probably acts as a genotoxic initiator in the multistep process of hepatocarcinogenesis, although the precise mechanisms involved have not been determined. Aflatoxin ingestion may also have an aetiological role in high incidence regions, probably as a genotoxic or epigenetic promoter to hepatitis B virus-initiated carcinogenesis. In low risk populations cirrhosis is the most important causal association of hepatocellular cancer. The cirrhosis is often the result of alcohol abuse, but the tumour may complicate all aetiological forms of this disease. Whether neoplasia is an inevitable consequence of the hyperplasia of cirrhosis, or the increased hepatocyte turnover rate acts as a promoter is not known. Hepatitis B virus infection plays a lesser part, and aflatoxin no part at all.