EXPRESSION OF SMOOTH-MUSCLE ACTIN IN CULTURED-CELLS FROM HUMAN PLASMACYTOID MYOEPITHELIOMA

Objective. The definition of plasmacytoid myoepithelioma, a neoplasm e xhibiting myoepithelial differentiation, has been recently questioned. To better understand the histogenesis of this neoplasm, we searched f or myoepithelial markers in histologic sections of plasmacytoid myoepi thelioma and in a cell line (M1) derived from this same neoplasm. Stud y design. Expression of vimentin, pan-keratin (AE-3) and smooth-muscle actin was studied by immunohistochemistry in paraffin-embedded tissue and by immunofluorescence in M1 cells. Results. Plasmacytoid myoepith elioma tumor sections showed vimentin and AE-3 reactivity, but evidenc e of smooth-muscle actin was not seen. The cell line derived from this tumor also produced vimentin and cytokeratin. In addition, all cultur ed cells expressed smooth-muscle actin. Conclusion. We demonstrated th at cells derived from a case of plasmacytoid myoepithelioma appear to show full myoepithelial differentiation in vitro. Thus, they are myoep ithelial-like cells in nature. The lack of myogenous differentiation i n vivo could be due to an inhibitory process mediated by the extracell ular matrix.