TKT and neoplasm: In recent years, we have constructed tumor specific TK expression and enhanced expression vectors using hTERT promoter and found that transfection of these vectors could specifically kill NPC and its stem cells in vitro and inhibit NPC exograft in null mice in vivo without damaging normal cells and mouse liver and kidney [5-7], indicating that inhibition of telomerase activity is a key step to in NPC treatment.