MUSCLE-SPECIFIC ACTIN EXPRESSION IN CHONDROBLASTOMAS

Chondroblastomas are unusual cartilage benign lesions of bone that hav e well-characterized histological features, We reviewed and immunohist ochemically examined the paraffin block material of 20 cases, and in s even tumors of this collection we found distinct cytoplasmic muscle-sp ecific actin positivity of some tumor chondroblasts and chondrocytes. Muscle-specific actin-positive cells had the histological and ultrastr uctural features typical of chondroblasts, Moreover, in their cytoplas m they contained bundles of microfilaments with focal densities, as is typical of myofilaments. We did not observe any basal lamina around t hese tells, which were surrounded by intercellular matrix of the carti lage tissue type, Therefore, ive suppose that muscle-specific actin-po sitive cells occurring in some chondroblastomas do not represent an ad mixture of myofibroblasts but chondroblasts with actin expression, The unusual immunophenotype of some chondroblasts might he the result of aberrant actin expression or of the plasticity of their phenotype modu lated by microenvironmental stimuli. It is a question of whether, anal ogously to the terminology of myofibroblasts, such cells could be desi gnated as myochondroblasts. Copyright (C) 1997 by W.B. Saunders Compan y.