Mesodermal mixed tumor. Diagnosis by analysis of intermediate filament proteins.

A 58-year-old patient presented with poorly differentiated adenocarcinoma, probably primary in the ovary and, later in the course of her illness, with pure pleomorphic rhabdomyosarcoma. There was no evidence by light or electron microscopy of a mixture of these two tumor types. Further analysis by immunoperoxidase demonstrated scattered desmin-positive (muscle) cells in the adenocarcinoma portion of the tumor, establishing the diagnosis of malignant mesodermal mixed tumor.