CXCL12 and hematologic disorder: Stromal cell-derived factor 1a (SDF-1α or CXCL12) was found to retain and support the HSCs in the BM via the SDF-1α/CXCR4 axis [12,13]. CXCL12 is constitutively secreted by marrow stromal cells, being the major source for CXCL12 in adults [14]. Less is known about its role in hematological malignancies and how it could be affected during chemotherapy. The existing studies have come to conflicting results [8,15].