GAS6 and cancer: For instance, osteoblasts may secrete CXC chemokine ligand 12 (CXCL12) [100,101], TGF-β [71], growth arrest-specific protein 6 (GAS6) [102], osteoprotegerin (OPG) [103], osteopontin (OPN) [104], and leukemia inhibitory factor (LIF) [105], to promote colonization and dormancy of disseminating cancer cells in bone marrow.