CXCL12 and acute lymphoblastic leukemia: Furthermore, in B-ALL patients, increased peripheral levels of CXCL12 and high expression of CXCR4 on leukemic pre-B cells contribute to their proliferation, survival and homing to the BM microenvironment, which is mediated by STAT5, Rac-1 GTPase and a unique p38MAPK signaling pathway (67, 146–148).