Malignant papillary cystadenoma lymphomatosum. Light and electron microscopic study.

A case of malignant papillary cystadenoma lymphomatosum was investigated by light and electron microscopy. Histologically, the tumor consisted mainly of a characteristic papillary cystadenoma lymphomatosum, but the feature of epithelial components varied greatly in separate portions of the tissue; papillary adenoma-, tubular adenocarcinoma-, acinic cell tumor- or oncocytoma-like features were observed, the tumor cells showing "atypia" in major components. Numerous intracytoplasmic inclusions were found in many oncocytic cells arranged in acinar structure, and stained with PAS, AZAN or Alcian blue. Electron microscopically, large numbers of very large, swollen and closely packed mitochondria were observed in almost all the tumor cells. The intraplasmic inclusions were composed mainly of a long dense body enclosed by a single unit membrane, and the contents constituted bundles of fine filament running parallel to the longer axis. The inclusions were often observed to unite with lysosomes and to co-exist with secretory granules in the cytoplasm.