Epithelial and cartilaginous differentiation in clear cell chondrosarcoma

Summary Clear cell chondrosarcoma is a rare cartilaginous bone tumor, and little is known about its pathology. We investigated the immunohistochemical expression profiles of cytokeratins (CAM5.2, AE1/AE3, CK7, CK8, CK18, and CK20), epithelial membrane antigen, SRY (sex-determining region Y)-box 9, type II collagen, runt-related transcription factor 2, and osteocalcin in clear cell chondrosarcoma and compared them with those in chondroblastoma, conventional chondrosarcoma, and osteosarcoma. Of 5 cases of clear cell chondrosarcoma, 3 demonstrated positive staining for AE1/AE3 and some form of cytokeratin in the clear cell component. Of the 5 cases, 4 strongly expressed SRY (sex-determining region Y)-box 9 in the clear cell component but weakly expressed it in the cartilaginous component. Of the 5 cases of clear cell chondrosarcoma, 3 expressed runt-related transcription factor 2 in both the clear cell and cartilaginous components, but no expression of osteocalcin was detected. In chondroblastoma, 8 of 13 cases expressed AE1/AE3, and other cytokeratins, such as CK7 (4/13), CK8 (6/13), CK18 (8/13), and CK20 (3/13), demonstrated a similar staining extensity pattern between the cellular and cartilaginous components. Clear cell chondrosarcoma and chondroblastoma have similar immunohistochemical features in that they both express epithelial and chondrogenetic markers. On the other hand, tumor cells of clear cell chondrosarcoma have no osteoblastic immunohistochemical expression in comparison with chondroblastoma.