Ribavirin is a nucleoside analog that inhibits the replication of both DNA and RNA viruses, including influenza type A and type B. Ribavirin, as ribavirin 5’-phosphate, affects virus-infected cells primarily by inhibiting the enzyme inosine 5’-monophosphate (IMP) dehydrogenase. It potently suppresses eIF4E-mediated oncogenic transformation of murine cells in vitro, of tumor growth of a mouse model of eIF4E-dependent human squamous cell carcinoma in vivo, and of colony formation of eIF4E-dependent acute myelogenous leukemia cells derived from human patients.