PTHLH and breast carcinoma: Production of PTH-rP by breast carcinoma cells in bone is enhanced by growth factors, such as transforming growth factor-beta (TGF-β) and insulin like growth factor-1 (IGF-1), originally generated by osteoblasts, deposited into bone matrix as inactive growth factor-binding protein complexes, and subsequently activated upon release from bone matrix by osteoclast-mediated bone resorption [1].