Malignant oncocytoma of the lacrimal sac: ultrastructure and immunocytochemistry.

Malignant oncocytoma of the lacrimal sac is a rare tumor. A third example is presented here. In addition to oncocytes, tumor acini also harbored a few mucin cells and myoepithelial cells. The presence of immunoreactive lactoferrin and secretory piece suggested a resemblance to parotid acinic cell carcinomas. The difference was marked by a compact acinar structure and myoepithelial cell differentiation in the oncocytoma.