应用免疫组化技术对１９例骨肉瘤和２１例骨巨细胞瘤标本进行了Ｐ２１表达检测。结果显示Ｆ２１存在于癌组织中，在骨肉瘤表达率为５２％，２１例骨巨细胞瘤２例呈阳性表达，此２例均为骨巨细胞瘤Ⅲ级，且又是复发病例。提示，在Ⅲ级骨巨细胞瘤病例中，ｒａｓ基因已经开始活化，其蛋白产物Ｐ２１过度表达。 Immunohistochemical technique was used to detect the expression of P21 in 19 cases of osteosarcoma and 21 cases of giant cell tumor of bone. The results showed that F21 was present in the cancer tissue, and the expression rate was 52% in osteosarcoma, and 21 cases of giant cell tumor of bone showed positive expression. The 2 cases were all grade III giant cell tumor of bone and they were also recurrent cases. It is suggested that in the case of grade III giant cell tumor of bone, the ras gene has already started to activate, and its protein product P21 is overexpressed.