Hepatocellular carcinoma (HCC) is the third leading cause of cancer–related deaths worldwide, mainly because of its poor prognosis. A valid and reliable mechanism-based prognostic biomarker is urgently needed. γ-Hydroxy-1,N2-propanodeoxyguanosine (γ-OHPdG) is an endogenous mutagenic DNA adduct derived from lipid peroxidation (LPO). We studied the relationship between hepatic γ-OHPdG and hepatocarcinogenesis in three animal models and the potential of γ-OHPdG to be used as a prognostic biomarker for recurrence in HCC patients after surgical resection. Tumor bioassays were conducted in Xeroderma pigmentosum group A knockout mice (Xpa-/-), diethylnitrosamine (DEN)-injected mice, and Long-Evans Cinnamon (LEC) rats, and all are prone to HCC development. We found that the increased γ-OHPdG levels in liver DNA correlated with HCC development in all three animal models. Furthermore, Theaphenon E treatment significantly decreased γ-OHPdG levels in the liver DNA of Xpa-/mice, and this decrease was closely associated with its remarkable effect to reduce HCC incidence (from 100% to 14%). Theaphenon E also effectively inhibited HCC development in DEN-injected mice. Using two independent sets of clinical samples from 90 and 45 HCC patients, our studies demonstrated that higher levels of γ-OHPdG in HCC biopsy specimens, detected by immunohistochemical staining , are strongly associated with low survival (p<0.0001) and low recurrence-free survival (p=0.007), respectively. These results support γOHPdG as a promising biologically relevant biomarker for predicting the risk of HCC and its recurrence. In this proposal, we propose in Aim 1 to extend these exciting findings to include a larger patient population to further address questions on γ-OHPdG’s relationships with (1) the underlying etiology of HCC, e.g. HBV, HCV, alcoholic liver disease, and non-alcoholic steatohepatitis (NASH) and (2) clinical predictors for aggressiveness, e.g. differentiation, HCC stage, vascular invasion, and extra-hepatic metastasis. We also want to compare its levels with those of the adjacent non-tumorous tissues and to examine the tumor mutation load. In Aims 2 and 3, we will develop a non-invasive method for detecting γ-OHPdG in human urine. Our hypothesis is that the adduct levels in urine reflect those in liver DNA. In Aim 4, we will conduct an intervention trial with Polyphenon E, an FDA approved equivalent of Theaphenon E, to prevent HCC recurrence in high risk patients identified with high liver γ-OHPdG. Our long-term goal is to develop γ-OHPdG as a prognostic biomarker for HCC and its recurrence for intervention trials.