CXCR4 and cancer: The secretion of C–X–C motif chemokine 12 (CXCL12), also known as stromal-derived factor 1 (SDF-1), by stromal cells in the bone marrow is known to attract osteotropic cancer cells via stimulation of the C–X–C chemokine receptor type 4 (CXCR4) receptor that is up regulated by many tumors.