PTHLH and breast cancer: Previous studies have shown that the osteolytic bone lesion, which is induced by metastatic breast cancer cells through secretion of bone catabolic factors including parathyroid hormone-related protein (PTHrP), interleukin (IL)-11, IL-8, and IL-6, in turn exacerbates this tropism by promoting cancer cell growth in the bone via growth factors released from the degraded bone matrix [4, 5].