The successful application of a non-oncogenic virus, Newcastle disease virus (NDV), which can be used to modify a highly metastatic tumor to become more immunogenic is reported. Such NDV modified tumor cells were found to be effective as tumor vaccine for anti-metastatic therapy in combination with surgical removal of the primary tumor. The protection in the animals seen after this treatment is paralleled by an establishment of specific systemic anti-tumor immunity. This protective immunity depended on recognition of a distinct tumor antigen. The therapy protocol also worked in animals bearing the plastic adhesive variant ESb-MP. It did not work, however, when using an immune escape variant not expressing a specific tumor antigen.