PTHLH and metastasis: Furthermore, a mathematical model was established to combine these indicators, so as to predict the risk of bone metastasis in patients with advanced lung cancer more accurately: logit (p) = − 8.4988 + 0.0211 * tP1NP + 0.0079 * PTHrP + 0.0016* OPG + 0.0021*β-CTx.