Clear cell adenocarcinoma of the tongue.

A firm, ulcerated tumor formed on the left side of the tongue of an elderly woman. Histopathological analysis showed that this unusual neoplasm was composed of monomorphic polygonal cells that exhibited a clear cytoplasm containing large amounts of periodic acid Schiff (PAS)-positive, diastase-digestive material. Most of the tumor cells stained immunohistochemically for Cytokeratin, high-molecular, CAM5.2, and epithelial membrane antigen (EMA), but were negative for alpha-smooth muscle actin, vimentin, glial fibrillary acid protein (GFAP), and S-100 protein. These findings supported a diagnosis of clear cell adenocarcinoma. Although patients with this type of tumor generally have a favorable prognosis, the tumor in our patient was fast-growing and contained a large number of Ki-67 positive cells, which are known to be highly proliferative. Thus, this case highlights the fact that even clear cell adenocarcinomas that are usually slow-growing should be investigated by conventional morphological techniques and their proliferative activity quantified in order to select the most appropriate treatment strategy.