CXCR4 and acute myeloid leukemia: In AML cells, BTK phosphorylation can be induced by SCF-CD117 signaling or activating mutations of G-CSFR (T618I or truncated Q741x) or FLT3 (with internal tandem duplication of the juxtamembrane region, FLT3-ITD) to mediate cell survival, proliferation and adhesion, and can also be elicited by SDF1-CXCR4 signaling to mediate cell migration and adhesion to stroma cells (44–47).