Breast cancer cells secrete cytokines, such as parathyroid hormone-related protein (PTHrP) [55], vascular endothelial growth factor (VEGF) [56], interleukin (IL)-6 [57], IL-8 [58] and IL-11 [59] (Figure 1), which are known bone modulators. The gene discussed is PTHLH; the disease is breast cancer.