TKT and cancer: OVs possess cancer selectivity and efficiently kill cancers because (i) OVs utilize the EGFR pathway, which is activated in cancerous cells; (ii) elevated TK in cancer cells promotes enhanced replication of vTk-deleted OVs; (iii) OV kills cancer by replicating within the cancer, so that it can be effectively used at lower concentrations to stop replication when all the host cancer cells are lysed; and (iv) cancer cells lysed by an OV can release debris containing tumor antigens, which triggers the immune system and leads to cytotoxic T-cell activation and cell-mediated immunity [41].