PTHLH and breast cancer: Breast cancer cells augment the activity of bone resorption via promoting the differentiation and podosome formation of osteoclasts by secreting transforming growth factor-beta (TGF-β), tumor necrosis factor-alpha (TNF-α), interleukins (ILs), and parathyroid hormone-related protein (PTHrP), which leads to osteolytic bone metastasis.