Spontaneous malignant myoepithelioma of the maxillary gland in a young adult male BALB/c F1 hybrid mouse.

A spontaneous tumor was observed in the maxillary gland of a 12-week-old male BALB/c F1 hybrid mouse. Histopathologically, the tumor invaded both the nasal cavity and maxillary sinus, and ethmoturbinates were destroyed. The majority of the tumor cells had oval nuclei with eosinophilic and vacuolar cytoplasm. Numerous mitotic figures and necrotic foci were also observed throughout the tumor. Immunohistochemically, almost all of the tumor cells were strongly positive for cytokeratin (WSS) and alpha-smooth muscle actin. However, tumor cells were negative for cytokeratin (CAM 5.2), suggesting that these tumor cells originated from myoepithelial cells. The present tumor was diagnosed as a malignant myoepithelioma of the maxillary gland. This is the first report describing spontaneous malignant myoepithelioma in the maxillary gland of a young adult BALB/c F1 hybrid mouse.