**1. Introduction**

312 Hepatocellular Carcinoma – Basic Research

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> Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide. The prevalence of HCC is still increasing in Asia and Africa, and represents a leading cause of death among patients with chronic liver diseases in industrial countries including Europe and North America (Llovet et al., 2003). The prognosis of HCC is considerably poor for following reasons: (1) aggressive treatment for HCC is not usually possible because most of the patients have impaired liver function, (2) hepatoma cells are refractory to standard chemotherapy drugs and radiation, and (3) HCC frequently recurs even after curative resection (Poon et al., 2009). Moreover, owing to the lack of reliable clinical HCC markers, fewer than 20% of patients are diagnosed at a stage where curative treatment can be performed (Llovet et al., 2003).

> HCC is unique among the various types of malignancies, in that it frequently arises in individuals with hepatitis B virus (HBV)- and C virus (HCV)-related liver cirrhosis. Although the precise mechanism of the relationship between the hepatitis viruses and hepatocarcinogenesis is unknown, recent studies have suggested that an aberrant response against DNA damage might be involved in HBV- and HCV-induced carcinogenesis, as observed in many types of cancer cells. Therefore, for future development of treatments against HCC, understanding the functional role of the DNA damage response (DDR) in HCC-prone individuals would be of value.
