Adenoid cystic carcinoma with myoepithelial predominance affecting maxilla and maxillary sinus.

Adenoid cystic carcinoma (ACC) represents less than 10% of all salivary gland tumors, rarely occurring centrally in the jaws. Herein we describe the case of a 36-year-old female patient presenting a painless swelling in the right maxilla, resulting in marked facial asymmetry. Intra-orally it was observed a swelling covered by an erythematous and irregular-surfaced mucosa, affecting the gingiva and crossing the midline of the hard palate. Imaging studies showed a mixed radiolucent-radiopaque lesion with ill-defined borders, involving the right side of the maxilla and the maxillary sinus. Incisional biopsy revealed basophilic cribriform tumoral islands and solid sheets of neoplastic cells invading bone trabeculae. Most of the tumoral cells presented myoepithelial characteristics, while few true luminal/epithelial cells were observed. To illustrate the epithelial-myoepithelial pattern, immunohistochemical reactions were performed, as well as double immunohistochemical staining. The diagnosis was intraosseous ACC, which features were discussed as well as the potential differential diagnosis.