In contrast to other tumor suppressor genes, loss of IRF-1 alleles alone rarely induces tumor development, however, IRF-1 deficiency was previously demonstrated to markedly enhance tumor predispositions caused by the expression of a c-Ha-Ras transgene or nullizygosity of the transformation-related protein 53 (Trp53) gene (32). This evidence concerns the gene IRF1 and neoplasm.