TKT and neoplasm: To determine the function of the exogenous CD and TK genes in tumor cells, the tumor cells with/without the pcDNA3-KDRp-CDglyTK system were treated with GCV and/or 5-FC, cellular survival rates were assayed with MTT method and calculated as the OD value of the pro-drug group/the OD value of the non-drug group × 100%.