Immunohistochemical staining of the tumor. A, The spindle cells exclusive of osteoclast-like giant cells were entirely positive for CD34. B, The spindle cells were also positive for CD31. C, Diffuse and strong expression of CK could be seen in the spindle cells. D, The tumor cells were negative for Actin(SM) in contrast to the positive expression of Actin(SM) in normal blood vessel. E, The CD68 staining highlighted the presence of osteoclast-like giant cells. F, Ki67 proliferative index was approximately 10%.