Among the clinical trials using HSV-1-tk, the safety and efficacy of HSV-1-tk (gene therapy) in combination with valacyclovir, radiotherapy and chemotherapy in newly diagnosed and recurrent glioblastoma multiforme and grade III astrocytoma are currently being investigated (NCT03596086, NCT03603405). This evidence concerns the gene TKT and astrocytoma (excluding glioblastoma).