TKT and neoplasm: On the other hand, Zhao et al., imitated recurrence using a genetically engineered murine GBM cell model with the HSV-TK suicide gene, in which the cell death program is activated after ganciclovir administration, allowing initial tumor expansion and partial regression in the deep area of the brain [42], and then revealed the increased invasiveness of rGBM cells and a higher ratio of monocyte-derived macrophages among the entire population of tumor-associated myeloid cells.