IGF1 and neoplasm: Our analysis of JHC7 cell proliferation in the presence of extracellular calcium, TGF-β1, or IGF-1 indicates that bone destruction and tumor expansion are linked in a positive-feedback loop: we propose that growing tumors provide increased numbers of osteolytic cells that dissolve bone, releasing factors such as calcium, TGF-β1, and IGF-1 that promote chordoma cell proliferation, which might enhance bone degradation.