Clear cell tumors of bone.

Except for clear cell carcinomas that metastasize to bone, with renal cell carcinoma being the principal representative of that group, clear cell osseous neoplasms are rare. The only distinct nosologic entity in this category that is primary in the bone is the clear cell chondrosarcoma (CCCS). This lesion, which is most often seen in the proximal femur or humerus, affects males more often than females and has a peak incidence during the third and fourth decades of life. Radiologic images of CCCS show a well-circumscribed, often calcified lytic lesion that may expand the bone, but only uncommonly breaches the cortex. Clear cell elements in CCCS are accompanied by "conventional" foci of chondrosarcoma in less than 50% of cases; noncartilaginous "secondary features," including areas of osteogenesis, osteoclast-like giant cells, and zones resembling aneurysmal bone cyst or giant cell tumor of bone, may be apparent as well. CCCS is a relatively indolent malignancy; roughly 25% of patients experience local recurrences of their tumors or suffer metastasis, but tumor-related death is uncommon, particularly when the lesion has been completely resected en bloc. Sporadic examples of other tumors in bone also may be focally or entirely composed of clear cells. These include osteosarcoma, chondroblastoma, chordoma, adamantinoma, Ewing's sarcoma, and primitive neuroectodermal tumor. The last two of these lesions represent the most common primary clear cell bone tumors in children, whereas metastatic renal clear cell sarcoma is the most frequent metastatic pediatric tumor in this category.