Recent evidence shows that Egr-1 can be rapidly induced by IR and protects cancer cells from IR-induced cell death by regulation of apoptotic-related genes Bax, p53 and AIF in glioma and colorectal cancer cell lines.22, 23 To obtain the insight into the role of Egr-1 in HCC cells upon IR exposure, we determined Egr-1 expression in response to different IR doses in HepG2 and SMMC-7721 cells. This evidence concerns the gene TP53 and central nervous system cancer.