It has been revealed that, by activating STAT3 signaling, IL-9 strongly induced tumor cell proliferation and migration, prevented tumor cells from apoptosis induced by IFN-γ, and facilitated the intercellular adhesion of tumor cells to pleural mesothelial cell monolayers (PMCs) via ICAM-1/LFA-1- and/or VCAM-1/integrin-β-dependent mechanisms. This evidence concerns the gene IL9 and neoplasm.