Another phase III clinical trial using retroviral vectors with HSV thymidine kinase (HSV‐Tk) gene and ganciclovir for GBM gene therapy was performed where HSV‐Tk acts as a suicide gene and converts ganciclovir to its active form, halting cell cycle progression and eventually leading to cell apoptosis.98 The gene discussed is TKT; the disease is glioblastoma.