Expression of tau proteins and tubulin in extraskeletal myxoid chondrosarcoma, chordoma, and other chondroid tumors.

Tau proteins are microtubule-associated proteins required for the polymerization of tubulin. The abnormal accumulation of tau proteins in neurofibrillary tangles is a well-known phenomenon and has been studied extensively. However, the role of tau protein in chondroid tissue and its neoplasia is unknown. In the present study, 2 extraskeletal myxoid chondrosarcomas (EMCs), 6 chordomas, 6 chondrosarcomas, 3 myxoid chondrosarcomas of bone, 2 osteochondromas, 6 chondroblastomas, and 2 nonneoplastic adult articular cartilages were immunostained with monoclonal antibodies against tau proteins and tubulin. The results showed that the coexpression of tau proteins and tubulin was present only in EMCs (2/2) and chordomas (4/6). Although tubulin was detected in chondroblastomas (5/6), osteochondromas (2/2), chondrosarcomas (5/6), and myxoid-chondrosarcomas of bone (3/3), tau expression was absent in these tumors. The perichondrial chondroblasts but not chondrocytes from nonneoplastic articular cartilage also localize tau and tubulin with a much weaker staining intensity. The results mainly demonstrate that there is frequent expression of tau proteins in some microtubule-rich neoplasms, such as EMC and chordoma. The different immunostaining pattern of tau proteins between chordoma and myxoid chondrosarcoma of bone may be useful in the differential diagnosis, especially when both neoplasms occur in the base of skull.