Clear Cell Odontogenic Carcinoma Harboring the EWSR1-ATF1 Fusion Gene: Report of a Rare Case.

Clear cell odontogenic carcinoma (CCOC) is a rare and aggressive malignant epithelial neoplasm, which occurs most frequently in the mandible of elderly patients. Morphologically, CCOC shares similar characteristics with other clear cell tumors, especially hyalinizing clear cell carcinoma of the salivary glands (HCCC). Both CCOC and HCCC are known to harbor EWSR1 rearrangements, especially the EWSR1-ATF1 gene fusion, which indicates a possible link between the two lesions. So far, this fusion has been demonstrated in five cases of CCOC in the literature. Herein, we add another CCOC case to the literature, which arose in the mandible of an 82-year-old female patient and was proven to harbor the EWSR1-ATF1 gene fusion. Immunohistochemically, this case was focally positive for CK7, CK14, CK19 and p63. The patient was referred to surgical treatment; however, she died of disease 2 months after the diagnosis, thereby demonstrating the aggressive nature of this tumor.