The paradox in our studies was that while oncolytic SFV vector VA7 effectively replicated in and destroyed a variety of IFN-responsive cancer cell lines in vitro, it consistently failed to eradicate tumors generated from the same cell types in vivo, even if large doses of virus were injected directly into the tumor mass and even if the tumors were void of visible physical barriers (Figure 3). This evidence concerns the gene IFNA1 and neoplasm.