Abstract： Objective To explore the predictive value of combined detection of serum carbohydrate antigen 125(CA125),cytokeratin 19 fragment antigen 21-1(CYFRA21-1),carcinoembryonic antigen(CEA),neuron specific enolase(NSE),and alkaline phosphatase(ALP)for bone metastasis in primary lung cancer patients.Methods A total of 104 lung canc-er patients who received treatment were collected as the observation group,and grouped into a bone metastasis group(50 cases)and a non bone metastasis group(54 cases)based on whether bone metastasis occurred.100 cases of benign lung lesions were collected as the control group.Clinical data of lung cancer patients were collected,the serum levels of CA1 25,CYFRA21-1,CEA,NSE,and ALP were detected in all subjects.Receiver operating characteristic(ROC)curve was applied to analyze the predictive value of serum CA125,CYFRA21-1,CEA,NSE,and ALP for bone metastasis in lung cancer patients.Multivariate Logistic regres-sion was applied to analyze the influencing factors of bone metastasis in lung cancer patients.Results Compared with the control group,the serum levels of CA125,CYFRA21-1,CEA,NSE,and ALP in the observation group were obviously increased(P＜0.05).The number of clinical stages Ⅲ～Ⅳ,number of lymph node metastasis,and serum levels of CA125,CYFRA21-1,CEA,NSE,and ALP in the bone metastasis group were obviously higher than those in the non bone metastasis group(P＜0.05).The AUC of serum CA125,CYFRA21-1,CEA,NSE,and ALP in predicting bone metastasis in lung cancer patients was 0.818,0.816,0.739,0.770,and 0.771,respectively,the AUC of combined detection of five tumor markers was 0.955,and the sensitivity,spe-cificity,and AUC were obviously higher than those of individual detection of each tumor marker(P＜0.05).Multivariate Logistic regression analysis showed that CA125,CYFRA21-1,CEA,NSE,and ALP were risk factors for bone metastasis in lung cancer pa-tients(P＜0.05).Conclusion The combined detection of serum CA125,CYFRA21-1,CEA,NSE,and ALP has high value in predicting bone metastasis in primary lung cancer patients,and the combined diagnosis has higher efficiency.