On the one hand, tumor cells release various factors that promote osteoclast activity and bone resorption, including the parathyroid hormone-related protein (PTHrP), lysophosphatidic acid (LPA), macrophage-stimulating protein (MSP), prostaglandin E2 (PGE2), interleukin-8 (IL-8), interleukin-11 (IL-11), matrix metalloproteinase-1 (MMP-1), CCN3, platelet-derived lysophosphatidic acid (LPA), and granulocyte–macrophage colony-stimulating factor [44,45,46,47,48]. Here, MMP1 is linked to neoplasm.