To test this hypothesis we developed a mathematical model of tumor-osteoclast interactions, including the cytokine fields of RANKL, OPG and PTHrP, and examined the model predictions by means of appropriate in silico experiments focusing on the following main questions: 1) How does the impact of systemic OPG compare to the impact of cancer–cell derived OPG production? The gene discussed is TNFSF11; the disease is neoplasm.