Two cases of intracranial germinoma showing a cell arrangement mimicking carcinoma.

Tumors of germ cell origin uncommonly arise in extragonadal sites. We report two cases of intracranial germinoma, in which it was necessary to distinguish between intracranial germinoma and metastatic carcinoma in cytological specimens. Cytologically, not only single tumor cells or loosely connective tumor cells but also closely packed clusters of cells and pair cells were recognized. Immunocytochemically, almost all tumor cells were immunoreactive for M2A, placental alkaline phosphatase, and c-kit. Closely packed clusters were also immunoreactive for pan-cytokeratin. Therefore, Cytopathologists should be aware that tumor cell clusters, mimicking carcinoma might appear in cytological specimens of intracranial germinomas. Although immunocytochemical analysis assists in correct diagnosis, some cell clusters showing cytokeratin immunoreactivity does not become the basis for the diagnosis of metastatic carcinoma. A panel of antibodies including D2-40, PLAP, and c-kit should be used.