In the normal CNS CXCL‐12 is constitutively expressed on endothelial cells and a small number of astrocytes, while in MS CXCL‐12 levels were shown to be high on astrocytes in both active lesions and at the edges of silent lesions where repair processes were taking place (Calderon et al., 2006). Here, CXCL12 is linked to myeloid sarcoma.