POORLY DIFFERENTIATED CARCINOMA OF THE PAROTID-GLAND IN A 6-WEEK-OLD SPRAGUE-DAWLEY RAT

A poorly differentiated spontaneous tumor was found in the parotid gla nd region of a 6-wk-old female Sprague-Dawley rat. The tumor consisted of undifferentiated cells forming dense clusters, well-defined nests, or compact sheets. In some areas, spindle-shaped cells were arranged in a fascicular fashion. Neither ductular nor acinar structures were s een. No keratinization was observed, either. Mitotic figures were freq uent. All neoplastic cells were immunoreactive for pankeratin bht nega tive for vimentin, alpha-smooth muscle actin and S-100 protein. Ultras tructurally, the tumor cells were characterized by desmosome-like junc tional complexes, poorly developed cytoplasmic organelles, and microvi lli-like cytoplasmic processes. Based on these findings and its anatom ical location, the present a tumor was diagnosed as a poorly different iated carcinoma of the parotid gland.