As shown in Tables 2 and 3, compared with non-transfected, untreated cells, transfection of control plasmid pGL3-basic-EGFP had no effect on survival rates of tumor cells 5-8F and MCF-7 with GCV treatment, and transfection of the enhanced plasmid pGL3-basic- hTERTp-TK-EGFP-CMV alone did not change the survival rates of tumor cells NPC 5-8F and MCF-7. Here, TKT is linked to neoplasm.