Expression of these genes in the primary tumor has multiple functions including: (i) targeting cells specifically to the bone microenvironment via homing factor CXCR4; (ii) facilitating colonization of the bone via expression of bone extracellular matrix degrading enzymes (MMP1, ADAMTS1); (iii) activating osteoclasts and favoring adhesion to the bone surface through OPN [15]. This evidence concerns the gene SPP1 and neoplasm.