PTHLH and breast cancer: In cancer-induced osteolytic bone disease, such as breast cancer metastases, cancer cells secrete a variety of cytokines and growth factors, including receptor activator of nuclear factor kappa-Β ligand (RANKL), IL-6, IL-8, interleukin 11 (IL-11), tumor-necrosis factor-alpha (TNF-α), vascular endothelial growth factor (VEGF), and parathyroid hormone-related protein (PTHrP) [32], which directly or indirectly stimulate osteoclasts to resorb bone.