In particular, PTHrP released by BC cells binds to osteoblasts via its receptor and then induces Receptor-Activator-of-Nuclear-factor-Kappa-B-Ligand (RANKL) up-regulation and Osteoprotegerin (OPG) down-regulation (in physiological conditions OPG acts as a decoy receptor binding the excess of RANKL). This evidence concerns the gene PTHLH and breast cancer.