CXCR4 and precursor B-cell acute lymphoblastic leukemia: In the homing of B cell progenitor ALL cells to the BM, CXCL12-mediated activation of p38MAPK was required [51], and those with high CXCR4 expression had more significant liver or spleen infiltration than those with low CXCR4 expression in pediatric B-ALL patients [46].