Tumor incidence in mice inoculated with HSV amplicon into pre-established EL4 tumor and growth of parental EL4 cells contralaterally. Viable EL4 cells (10⁶) were implanted SC on both hind limbs of 8-week-old C57BL6 mice. Tumors were allowed to develop to a size of 5 to 6 mm diameter. HSV amplicon virus (2 × 10⁶ amplicon-containing virus particles) was injected into the right tumor on days 7 and 14, and growth of the HSV amplicon-treated (▪) and untreated EL4 tumor (□) was monitored every 3 days. Growth of HSVlac-treated tumor (•) or contralateral untreated EL4 tumor (▵) are also shown. Each experimental group consisted of 10 mice. The graph represents the percentage of tumor-bearing mice over time. Mice were killed when the tumor diameter exceeded 22 mm.