Nasopharyngeal Hyalinizing Clear Cell Carcinoma: Report of the Histopathologic Features of a Case Showing EWSR1 Rearrangements by FISH and Literature Review

Background. Hyalinizing clear cell carcinoma (HCCC) is a rare low-grade malignant tumor affecting the minor salivary glands; nasopharyngeal involvement is uncommon. Methods and Results. A 38-year-old male patient presented with a 3.2 x 4.5 x 4.4 cm expansile mass obliterating the lumen of the nasopharynx and extending into the left nasal cavity. Histopathologically, the tumor was characterized by clear round to polygonal epithelial cells arranged in anastomosing trabeculae and solid nests. The stroma consisted of fibromyxoid connective tissue with areas of intense hyalinization and desmoplasia. Immunohistochemically, strong and diffuse reactivity for AE1/AE3, CK5/6, and p63 was observed. EWSR1 gene rearrangement was confirmed by fluorescence in situ hybridization. The diagnosis of nasopharyngeal HCCC was rendered. Surgical excision was performed along with adjuvant radiotherapy and chemotherapy. Conclusions. HCCC generally demonstrates good prognosis with low metastatic potential. Identification of EWSR1 gene disruption is useful in discerning HCCC from other neoplasms with overlapping microscopic features.