TKT and cervical cancer: Different gene-directed enzyme prodrug systems such as cytosine deaminase (CD)/5-flurocytosine (5-FC), herpes simplex virus thymidine kinase (HSV-TK)/ganciclovir enzyme (GCV) [81], nitroreductase (NTR)/CB1954 [82], and uracil phosphoribosyltransferase (UPRT)/5FU [83] have been used as therapeutic weapons in cervix cancer.