TYPE X COLLAGEN EXPRESSION AND HYPERTROPHIC DIFFERENTIATION IN CHONDROGENIC NEOPLASIAS

Little is known about matrix biochemistry and cell differentiation pat terns in chondrogenic neoplasms. This is the first description of the focal expression of collagen type X by neoplastic chondrocytes in situ and its incorporation into the extracellular matrix of cartilaginous tumors. This shows that neoplastic chondrocytes have the potential to undergo the full program of cell differentiation, including hypertroph y, comparable to their physiological counterparts in the growth plate. However, only in benign osteochondromas was a zonal expression of typ e X collagen found similar to that observed in the growth plate, where the cells immediately above the ossification frontier are selectively positive for type X collagen. In enchondromas and chondrosarcomas, th e expression was randomly distributed within the tumors. Surprisingly, in less differentiated chondrosarcomas with spindle-shaped cells and non-cartilaginous extracellular matrix, exceptional expression of coll agen type X was observed, which indicates potential uncoupling of coll agen type X expression from the differentiated chondrocytic phenotype in neoplastic chondrocytes in vivo.