IL9 and B-cell chronic lymphocytic leukemia: Hence, while the potential effects of IL-9 dysregulation on other components of the tumor microenvironment remain to be clarified, we can definitely qualify IL-9 as a pro-tumoral cytokine in the CLL context, with both autocrine pro-survival effects on leukemic cells, indirect pro-chemotactic effects through paracrine conditioning of neighboring stromal cells, and long-distance effects on stromal cells far from the lymphoid tumor microenvironment in order to generate new leukemic foci.