Recombinant adenovirus expressing HSV-TK under the control of ERE73 (1 + 2)-ARF (−13) and ERE73 (3 + 4)-ARF (−13) induced efficient HSV-TK gene expression in cancer cell lines but not in normally growing cells (Figure 3B), and showed cancer cell-specific cytotoxicity in vitro and in vivo (Figure 3A and Figure 4B,C). This evidence concerns the gene TKT and cancer.