Immunoblot of SUM149 tumor lysates revealed that PVSRIPO treatment increased intratumoral expression of the following: 1] iNOS, an enzyme responsible for producing NO; 2] myeloperoxidase, an enzyme predominately expressed by neutrophils that catalyzes the production of cytotoxic free radicals; 3] p-Stat1 (Y701), phosphorylated downstream of both type-I and -II IFN signaling; and 4] Stat1, which is induced by its own phosphorylation (Figure 5C). This evidence concerns the gene MPO and neoplasm.