Discussion:

Hyalinizing clear cell carcinoma (HCCC) is a rare minor salivary gland tumor of female predominance. The majority of HCCCs present as a mass inside the oral cavity and is presumed to arise from minor salivary glands, though a minority can present as major salivary gland, nasopharyngeal or laryngeal tumors, as well. The most common sites of origin are the palate and tongue base. The mobile tongue and other minor salivary gland locations can also be seen. The tumors are typically submucosal and present as a swelling, though they can occasionally ulcerate. The lesions are often found on routine dental examination, and the majority of patients have a short history before presentation.

Grossly, the tumor size ranges from 1.0-4.5cm and has a white-tan cut surface. Cystic changes are unusual. HCCCs can appear relatively circumscribed but they lack encapsulation and can show infiltration of surrounding tissues. Histologically, there is a wide range of appearance. The clear cell predominance seen in this case is in the minority, as tumor cells may often have a majority of pale eosinophilic cytoplasm, or they a mixture of both eosinophilic and clear cytoplasm.

As a diagnosis of exclusion, any evidence of myoepithelial differentiation and histomorphologic features of other salivary gland neoplasms must be considered. Though not performed in this case, most tumors are diffusely positive for pancytokeratin, and can be focally positive for EMA, CK7, CK19, and CAM5.2. Recent evidence shows a consistent EWSR1-ATF1 genetic fusion which may also serve as a useful diagnostic marker.

HCCC is considered low grade, by definition, and the vast majority have had good outcome. Treatment usually involves primary resection, if the tumor is in an accessible location, and/or primary radiation.