Objective:To investigate the expression and significance of cancer inhibitory gene PTEN protein in osteosar- coma.To analyze the level of its expression in different histological classification of osteosarcoma.To determine the possibility of taking PTEN protein as a marker gene for diagnosing osteosarcoma.To observe the clinical value of PTEN expression levels as a reference index for osteosarcoma classification.Methods:43 specimens collected from osteosarcoma excision were studied.30 specimens collected during the same period from benign lesion of bone(osteochondroma)operation were taken as the control group.Immunohistochemistry staining(Elivison~(TM)two steps method)was used to detect the expression of PTEN protein in 43 cases of osteosarcoma.SPSS 10.0 was used in statistical analysis.Results:immunohistochemistry staining showed that the positive reaction of PTEN protein was all oriented to cytoplasm,which were brown or yellowish- brown granules.By way of X~2 test,the significant difference of the positive expressions of PTEN protein between bone benign lesion and osteosarcoma(X~2=7.976,P<0.01)was observed.Osteosarcoma with different degrees of histodifferentiation showed different level expression of PTEN protein.There was significant difference between well-differentiated osteosarcoma (gradesⅠ-Ⅱ)and poorly-differentiated osteosarcoma(gradeⅢ)statistically(P<0.01).The level of expression of PTEN was negatively correlated to the histological grade of osteosarcoma.There was great significance statistically(r_s=-0.4922,P<0.01).Conclusion:PTEN protein may be used as candidate gene of cancer inhibitory gene:PTEN protein is a cancer sup- pressor gene protein which has expression in bone tumors.It might not only be used in the study of pulmonary carcinoma and neurogliocytoma,but also in the study of bone tumor;the expression of PTEN is related to benignancy or malignancy of bone tumor and their degree of differentiation.The expression of PTEN is positively correlated with degree of differentiation. Objective: To investigate the expression and significance of cancer inhibitory gene PTEN protein in osteosar-coma. To analyze the level of its expression in different histological classification of osteosarcoma. To determine the possibility of taking PTEN protein as a marker gene for diagnosing osteosarcoma. To observe the clinical value of PTEN expression levels as a reference index for osteosarcoma classification. Methods: 43 Tensor collected from osteosarcoma excision were studied. 30 specimen collected during the same period from benign lesion of bone (osteochondroma) operation were taken as the control group. Immunohistochemistry staining (Elivison ™ two steps method) was used to detect the expression of PTEN protein in 43 cases of osteosarcoma. PSS 10.0 was used in statistical analysis. Results: immunohistochemistry staining showed that the positive reaction of PTEN protein was all oriented to cytoplasm, which were brown or yellowish-brown granules.By way of X ~ 2 test, the significant dif ference of the positive expressions of PTEN protein between bone benign lesion and osteosarcoma (X ~ 2 = 7.976, P <0.01) was observed. Osteosarcoma with different degrees of histodifferentiation showed different level of expression of PTEN protein. There was a significant difference between well-differentiated The level of expression of PTEN was negatively correlated to the histological grade of osteosarcoma.There was great significance statistically (r_s = -0.4922, P <0.01) 0.01) .Conclusion: PTEN protein may be used as candidate gene of cancer inhibitory gene: PTEN protein is a cancer sup- pressor gene protein which has expression in bone tumors. It might not only be used in the study of pulmonary carcinoma and neurogliocytoma, but also in the study of bone tumor; the expression of PTEN is related to benignancy or malignancy of bone tumor and their degree of differentiation. the expression of PTEN is positively correlat ed with degree of differentiation.