IL-17 promotes the differentiation of Th9 cells by up-regulating the expression of interferon regulatory factor 4 (IRF4) and GATA-3, accelerating the release of IL-9, recruiting more inflammatory cells to the site of tumour cells, and activating the immune response of the CD8+ T lymphocytes [19], thus inhibiting Tregs functionality and reducing MPE formation and mortality in MPE-bearing mice. This evidence concerns the gene IRF4 and neoplasm.