CXCL12 and acute lymphoblastic leukemia: Although the SDF‐1/CXCR4 pathway is critical for the homing to and retention of leukaemia cells in the BM, drug‐resistant MLL‐AF9 AML cells in BM were not affected by AMD3100, and BCP‐ALL cell chemotaxis towards the leukaemia niche was independent of SDF‐1/CXCR4.