The Epidemiology of Human Liver Tumors

The epidemiology of primary liver cancer is reviewed in relation to associated lesions, e.g., cirrhosis, chronic hepatitis. Little data are available to permit evaluation of the frequency of many preneoplastic and precirrhotic lesions which per se carry a low mortality. The proportion of cirrhotic livers in which primary cancer develops varies between countries due to etiological differences. The major factors suspected of causing cirrhosis and cancer in man are: i) hepatitis B, ii) aflatoxin, and iii) alcohol. There is a miscellaneous group of hepatoproliferative disorders due to a wide range of agents which form a small proportion of the total liver problem in industrial and non-industrial states. In contrast to rodents, few liver carcinomas are related to industrial or occupational factors, apart from an association with alcoholism and low socioeconomic class. Data on benign hepatocellular proliferative lesions are inadequate, apart from steroid-induced adenomas. In contrast to rodent studies, primary liver cancers have not been associated in man with enzyme inducers, such as pesticides or drugs. In conclusion, apart from aflatoxin and hepatitis B, it has proven difficult to make valid comparisons between experimental models and human liver cancer and disease except in relation to morphological pathogenetic pathways. This discrepancy between high frequency or experimental carcinogens identified in rodents and the rarity of demonstrating similar effects due to chemical exposures in man merits further consideration.