Tumor volume analysis after treatment in BALB/c nude mice. Implanted tumors were generated by injecting MCF-7 cells in the flank in BALB/c nude mice. When subcutaneous tumors reached approximately 7–8 mm in diameter, rAAV/TRE/HSVtk/Tet-On virus (2 × 1011 particles/ml) or mock-infection (DMEM) were performed direct intratumor injection to human breast cancer model on day 0, followed by a second injection on day 7. GCV treatment (100 mg/kg) was started on day 0 and continued for another 14 days after induced by Dox for one week. Tumor size was measured every 3 days. Tumor volume values (mm3) are expressed as means ± SD. The tumors of the rAAV/tk/On+Dox+GCV group demonstrated significant tumor growth suppression after GCV treatment compared with mock (P < 0.05 on day 30 after infection).