An immunohistochemical study of adenoid cystic carcinoma of the external auditory canal.

Specimens from five cases of adenoid cystic carcinoma of the external auditory canal were studied by immunohistochemical staining, and findings were compared with those from adjacent non-neoplastic tissues containing ceruminous glands. In the ceruminous gland, cytokeratin showed diffuse positive staining, while myoepithelial cells were stained for smooth muscle actin, desmin, S-100 protein and vimentin. The epithelial markers used were cytokeratin, carcinoembryonic antigen and secretory component and stained at various densities the inner cells of the tubular component and duct-lining cells in the cribriform component of tumor tissues. In contrast, the muscular markers, smooth muscle actin and desmin, and the mesenchymal marker, vimentin, were positive in the outer cells of the tubular component and in the cyst-lining cells of the cribriform component. S-100 protein immunoreactivity showed paradoxical results; positive findings occurred in the myoepithelial cells of the ceruminous glands and in the inner cells of the tubular component and duct-lining cells of the cribriform component of the tumor. Present findings demonstrate that adenoid cystic carcinoma of the external auditory canal had dual epithelial and myoepithelial differentiation and can mimic the ceruminous glands of the auditory canal.