Many of the molecules driving homing and retention of leukemic cells in tissues have been identified (54, 55); among them, the CXCL12/CXCR4 axis has been shown to be essential for hematopoietic stem cell (HSC) migration and homing and also for cancer cell migration and metastasis (3, 20, 56). This evidence concerns the gene CXCL12 and cancer.