Cancer Risk Reduction

An overwhelming body of data across species has demonstrated the potency of AFB1 as a carcinogen and mutagen.32 The best evidence indicating an interaction between hepatitis B virus (HBV) and aflatoxin in human liver cancer has come from a cohort study in Shanghai, China, involving more than 18,000 men.54 5674 Assays for urinary AFB1, its metabolites AFP1 and AFM1, DNA adducts, and hepatitis B surface antigen (HBsAg) status have been undertaken. Subjects with liver cancer were significantly more likely than controls to have detectable concentrations of the aflatoxin compounds. Positivity for HBsAg was strongly associated with liver cancer risk. Thus, aflatoxin exposure in the presence of a persistent HBV infection increases the risk of human liver cancer.28

Such factors as unknown genetic and host response interactions may play a role in the liver cancer/HBV/AFB interaction.28 33 Evans et al.20 compared three independent cohorts of male HBsAg carriers in Senegal, in Haimen City, China, and among HBsAg carriers in the United States (largely Asian origin). The risk of liver cancer in China (878 per 100,000 person-years [py]) was dramatically higher than in Senegal (68 per 100,000 py) or among United States HBV carriers (330 per 100,000 py). The prevalence of HBsAg was only moderately higher in Senegal (20% vs. 16%) than in China, and the level of aflatoxin exposure was expected to be higher in the African setting.

Vaccination for HBV has been shown to drastically reduce liver cancer risk in some populations. JECFA34 has recommended that vaccination for HBV must take high priority in preventing HCC. There are many HBV carriers (approximately 360 million worldwide). In addition, about 110,000 cases of HCC cases yearly worldwide have been attributed to hepatitis C virus infection (HCV). Access to HBV vaccine is incomplete, especially in developing countries; no vaccine is available for HCV as yet.

The experience of Korea in reducing adult liver cancer by vaccination for HBV is an excellent example of vaccination importance. The prevalence of HBV infection and HCC is high (about 21 per 100,000); aflatoxin contamination is relatively high. In 370,000 males followed for more than 3 years, HBV vaccination drastically reduced HCC (incidence of 215 cases/100,000 vs. 8 cases/100,000).39 This reduction in HCC cases was accomplished without any additional resources being expended on reducing aflatoxins in the food supply and without any change in aflatoxin regulations.

In Taiwan, an area of hyperendemic infection and moderate to high aflatoxin exposure, the immunization program against HBV reduced the rate of liver cancer in children 6 to 14 years of age from 0.7 per 100,000 between 1981 and 1986 to 0.57 between 1986 and 1989, and then to 0.36 from 1990 to 199433. Because the incidence of liver cancer peaks in the sixth decade of life in Taiwan, at least 40 years may be required to see an overall decrease in the rate of liver cancer as a result of the vaccination program.

Both these populations should be followed in future years to further elucidate the relationship among aflatoxin, liver cancer, and HBV. These studies lend support to the hypothesis that the carcinogenic potency of aflatoxin may be reduced in humans by vaccination for HBV, as pointed out by JECFA.33 The possibility should be considered that in the case of liver cancer scarce public health resources in developing countries may better be used for HBV vaccination programs (and thereby reduce incidence of liver cancer) than to lower aflatoxin levels to those required in the European Union. However, the effects of chronic exposure to relatively high levels of aflatoxins on growth and development of children should also be considered, and cost-effective methods to monitor and mitigate this exposure are needed.

10 Ways To Fight Off Cancer

10 Ways To Fight Off Cancer

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