GENETIC EPIDEMIOLOGY OF PRIMARY HEPATOCELLULAR CARCINOMA

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The risk of common cancer is produced through gene-gene, and/or gene- environment interactions. These interactions are poorly understood for most cancers in part due to the diversity and complexity of the exposures. Primary hepatocellular carcinoma (HCC) represents a unique opportunity to investigate a complex cancer phenotype in humans. Epidemiologic studies have firmly established the role of chronic hepatitis B virus infection (HBV) and aflatoxin B1 (AFB1) exposure as environmental risk factors. These exposures are well described and are amenable to exposure assessment. it is therefore conceptually possible to examine their relationship to host genetic constitution in determining HCC susceptibility. Significant progress has been made during the current funding period toward understanding the genetic components of the HCC complex phenotype. Statistical analyses has demonstrated familial aggregation consistent with genetic susceptibility of HCC. Comprehensive genome-wide allele loss studies have identified multiple regions which could contain novel tumor suppressor genes. An interaction between host genetic constitution, HBV/AFB1 exposures, and HCC was established in c case-control study and confirmed in a cohort-derived study population. It is the goal of the of the current application to continue the integrated genetic epidemiologic analysis of HCC. Familial aggregation of HCC and its relationship to HBV and AFB1 exposure will be examined in a significantly expanded collection of families. Comparative genome hybridization (CGH) will be added to permit the localization of putative tumor suppressor genes and oncogenes. Regions observed to have high frequency changes in tumors will be studied by genetic mapping methods to assess their role in familial transmission. The role of genetic variability in candidate genes that modulate responses to HBV infection and AFB1 exposure will be assessed. This will be accomplished by expressing human xenobiotic metabolizing P450 cDNAs and their polymorphic variants in Saccharomyces cerevisiae and determining which ones in combination with AFB1 cause genetic alterations. Human gene mapping methods using a family-based case-control population will be used to test the role polymorphic variants of candidate AFB1 metabolizing loci in HCC. The influence of lipotrope insufficiency and genetic variability in lipotrope metabolism to HCC related end-points will be assessed. Finally, the interaction of major susceptibility genes, risk modifying loci, and environmental exposures and their role in determining risk and familial aggregation will be examined.