CXCL12 and neoplasm: Tumours produce granulocyte colony-stimulating factor (G-CSF) which skews the neutrophil retention/release balance in bone marrow, leading to this increase in blood neutrophils.3 G-CSF downregulates chemokine receptor type 4 (CXCR4) expression in human myeloid lineage cells, reducing their response to the bone marrow retention signal stromal cell-derived factor 1 (SDF-1).4