PTHLH and breast cancer: In breast cancer, TGF-β released from the matrix as a result of increased bone resorption can cause tumor cells to produce growth factors such as parathyroid hormone-related protein (PTHrP) and interleukin 11 (IL-11) that can perturb the RANKL/OPG balance, resulting in further osteoclastogenesis and perpetuation of osteolytic disease [2] (Figure 2).