Tumor slices stained with hematoxylin and eosin. Subcutaneous tumors were excised from BALB/c nude mice with different treatments under sodium pentobarbital (50 mg/kg, i.p.) anesthesia. Tumors were rinsed twice in normal saline (NS) then fixed in 4% polyparaformaldehyde for 12 hours, embedded in paraffin, sliced and sections stained with hematoxylin and eosin for light microscopic observation (× 400 magnification). A: DMEM group; B: GCV+Dox group; C: GCV+Virus group; D: Dox+GCV+Virus group.