TKT and neoplasm: Mice receiving LSL-hK-rasG12D-IRES-HSV1-tk GFF cells did not exhibit any tumor growth during the course of 11 weeks, while mice inoculated with Lox-hK-rasG12D-IRES-HSV1-tk GFF cells resulted in palpable tumors within 2 weeks, with tumor formation incidence of 40% during 11 weeks (2/5).