Hepatocellular carcinoma (HCC) is a major cause of cancer morbidity and mortality in many parts of Asia, including China and Thailand, and in sub-Saharan Africa, where there are upwards of 600,000 new cases and deaths each year. The impact of HCC is exacerbated by a median age of diagnosis of between 45 and 50 years and it is nearly always fatal. The major known etiological factors associated with development of HCC in these regions are infection with hepatitis B (HBV) and/or hepatitis C (HCV) virus and lifetime exposure to high levels of aflatoxin B1 (AFB1) in the diet. HCC is also the most rapidly rising solid tumor in the US and is overrepresented in minority communities. While knowledge of the etiology of HCC has spurred many mechanistic studies to understand the pathogenesis of this disease, this information is only just beginning to be translated into development of preventive and clinical interventions in high risk populations. The goals of this project are to develop and validate biomarkers reflecting the biological effects of exposures to chemical and viral toxicants in the etiology of liver cancer. In all chronic human diseases, including cancer, ambient exposures to multiple environmental agents are significant contributors. The specific aims of this project are: 1) To develop validated isotope dilution LC-MS methods for urinary aflatoxin metabolites: oxidized aflatoxins; aflatoxin mercapturic acid; the imidazole-ring opened FAPY adduct and aflatoxin-lysine adducts; 2) To determine the power of mutations in hepatitis B virus (HBV) and p53 in serum DMA to predict HCC risk in cohorts in rural China and West Africa; and 3) To extend our assessment of interactions among hepatitis C virus (HCV), HBV and aflatoxin exposure as risk factors for HCC development in a cohort in Northern Thailand. This project is working to develop innovative quantitatitive methods for biomarkers that are applied to the assessment of the efficacy of both primary and chemoprevention interventions in high-risk populations for HCC. These biomarkers have been and will continue to be validated using cohort studies and their relation to disease risk will then be characterized.