This project will continue to focus on the identification of environmental and genetic risk factors for development of hepatocellular carcinoma (HCC) in Taiwan. We have demonstrated that, in conjunction with hepatitis B or C virus (HBV and HCV) infection, aflatoxin B1 (AFB1), 4-aminobiphenyl, and polycyclic aromatic hydrocarbons (PAH), increase HCC risk. Synergistic interactions between virus and chemical were also observed. Deletion o glutathione S-transferase M1(GSTM1) further increased risk in exposed subjects. The current proposal will focus on a case-control study nested in a cohort established by our collaborator Dr. Chien Jen Chen in which 25,611 subjects were recruited and a total of approximately 350 HCC cases will be identified by the end of the next four years. We will analyze blood samples from cases and controls for urinary aflatoxin metabolites and AFB1- and PAH-albumin adducts as markers of exposure. We will also begin to investigate the role of oxidative stress in risk for HCC by analyzing for variants in genes that encode enzymes with pro-oxidant and anti-oxidant activities. damage from ROS and carcinogenic metabolites that are not detoxified may be prevented from contributing to carcinogenesis by DNA repair; thus, we will extend our investigation of genetic susceptibility to DNA repair genes in the base excision and nucleotide excision repair pathways. We hypothesize that cases will more frequently be carriers of "higher risk" alleles than controls and that there will also be an interaction between environmental exposures and genotype. Finally, we will carry out a small exploratory study to determine whether tumor DNA can be detected in plasma of HCC cases. Other studies have demonstrated that tumor DNA circulating in blood contains the same genetic alterations as are found in the tumor. We will begin to investigate this phenomena in our HCC cases specifically looking at p.53 mutations and methylation of p16. These pilot studies will allow us to determine whether tumor DNA can be found at a high enough frequency to be useful in diagnosis and studies of etiology, when in the cancer process they are detectable.