Primitive neuroectodermal tumor arising in an ovarian mature cystic teratoma: immunohistochemical and electron microscopic studies.

The occurrence of a malignant neuroectodermal tumor in a mature cystic teratoma is extremely rare. Five cases of ovarian primitive neuroectodermal tumors (PNET) or neuroepitheliomas have been reported. In two, the tumor was adjacent to foci of a mature teratomatous element. We present the immunohistochemical profile and electron microscopic study of an ovarian mature cystic teratoma with PNET or malignant neuroepithelioma. The transition between the mature neural elements and the malignant PNET presents a model for monodermic neuroepithelial differentiation and explains the histogenesis of this unusual tumor.