PTHLH and neoplasm: The release of insulin-like growth factor-1 (IGF-1) and TGF-β from bone matrix, in turn, acts on tumor cells: IGF-1 promotes tumor cell proliferation and inhibits apoptosis, while TGF-β induces the tumor to secrete more PTHrP, activating more OCs, and dissolving the bone matrix again (32), forming a “vicious cycle” that promotes the occurrence and development of tumor bone metastasis.