However, therapy for aggressive feline fibrosarcomas is often insufficient for complete and long lasting tumor eradication and more gene transfer studies involving various established feline fibrosarcomas should be conducted in order to understand if these viral vectors (Ras-DN, Rb, Mda7/IL24) could be applicable regardless of the origin (spontaneous vs. vaccine induced) of feline fibrosarcomas. This evidence concerns the gene RB1 and fibrosarcoma.