Chondroblastoma is an osteoid-forming, but not cartilage-forming neoplasm

Chondroblastoma is defined as a 'benign tumour, characterized by highly cel lular and relatively undifferentiated tissue composed of rounded or polygon al chondroblast-like cells' and the 'presence of cartilaginous intercellula r matrix' (WHO). An extensive analysis of the extracellular matrix composit ion and gene expression pattern of a large series of chondroblastoma cases shows, however, that type II collagen, which is the main component of any c artilage matrix, is not expressed by the neoplastic cells of this tumour en tity and is not deposited into the extracellular tumour matrix. Instead, os teoid and fibrous matrix is formed, with its typical biochemical compositio n. The multifocal expression of aggrecan proteoglycan in most chondroblasto mas explains the bluish, pseudo-chondroid appearance of some of the matrix- rich areas of chondroblastomas, This study did not show chondroid matrix fo rmation or chondroblastic cell differentiation in chondroblastomas, suggest ing that chondroblastoma should be classified as a specific bone-forming, r ather than cartilage-forming neoplasm, Copyright (C) 1999 John Wiley: & Son s, Ltd.