Aflatoxins as risk factors for hepatocellular carcinoma in humans.

On a global basis, primary liver cancer (PLC) is a very prevalent form of cancer. Wide variation of PLC incidence in different areas of the world suggests the involvement of environmental factors in its etiology. Two major classes of risk factors have been identified. Extensive evidence indicates the importance of infection by the hepatitis B virus as a major risk factor for PLC. Because many organic chemicals induce liver cancer in experimental animals, those to which human exposure is known to occur are also of interest with respect to their possible involvement as risk factors for PLC. Particular emphasis has been placed on aflatoxins because of the frequency with which they occur as food contaminants, together with their potency as liver carcinogens for a large number of experimental animals, including subhuman primates. Other mycotoxins, notably sterigmatocystin and fumonisin, also are relatively potent carcinogens for the liver of animals, but little is known about human exposure to them. Epidemiological surveys carried out over the past 25 years in Asia and Africa have revealed a strong statistical association between aflatoxin ingestion and PLC incidence. The combined experimental and epidemiological evidence has led to designation of aflatoxins as human carcinogens according to International Agency for Cancer Research criteria. Collectively, current evidence strongly suggests that PLC is of multifactorial origin, with probable interactions between viral and chemical agents in populations concurrently exposed to both classes of risk factors. Recently developed methods that permit individual monitoring of aflatoxin exposure, hepatitis B virus infection, and genetic damage caused by these agents are being applied in the design of molecular and biochemical epidemiological studies of the etiology of the disease. Application of this methodology may contribute to elucidation of the relative importance of interacting etiological agents in different populations.