Metastases of primary cancers known to cause osteolytic lesions, specifically breast cancer, secrete biological mediators including parathyroid hormone-related protein (PTHrP), interleukin (IL)-11, IL-8, and IL-6 [19,37], which induce osteoclast mediated bone resorption through activation of the RANK/RANKL/OPG signalling pathway [20]. The gene discussed is PTHLH; the disease is breast cancer.