So-called neoplastic myoepithelial cells in chondroid syringomas/mixed tumors of the skin: their subtypes and immunohistochemical analysis.

An immunohistochemical study of nine cases of chondroid syringomas/mixed tumors of the skin was performed to elucidate the nature of the so-called neoplastic myoepithelial cells (NMEC) in tumor tissues. These nine tumors contained NMEC of considerable variability in number from one tumor to another. These NMEC were classified into three types: (i) hyaline cells (plasmacytoid cells); (ii) spindle NMEC; and (iii) polyhedral cells. They showed different immunostaining patterns, as the following describes. Cytokeratin 14 was positive in most of the spindle NMEC and a large number of the polyhedral cells, and in a small number of the hyaline cells. Concerning low molecular weight cytokeratins, most of the hyaline cells showed immunoreactivity, whereas they were negative in many of the spindle NMEC and were expressed only in a small number of the polyhedral cells. alpha-Smooth muscle actin and muscle-specific actin were positive in the spindle NMEC but negative in any of the hyaline cells and polyhedral cells. These findings strongly indicate that the hyaline cells and the spindle NMEC are of the simple epithelial and myoepithelial types, respectively. The findings also suggest that the polyhedral cells show differentiation toward basal cells of the sweat gland dermal ducts or myoepithelial cells.