Hyalinizing Clear Cell Carcinoma of Salivary Glands: A Retrospective Study Focused on Uncommon Morphology, Immunohistochemistry, and Detection of Gene Fusion Using Fluorescence In Situ Hybridization

Abstract Aims To investigate histological, immunohistochemical, and molecular features, especially uncommon morphology of hyalinizing clear cell carcinoma (HCCC) to expand the morphological spectrum of HCCC. Methods and results We examined 5 cases of HCCC by histological, immunohistochemical, and molecular analysis. Generally, 5 HCCC cases shared similar characteristics, exhibiting clear to slightly eosinophilic cells arranged in cords, nests, islands, or trabeculae with a hyalinized stroma, while myxoid stroma, perineural invasion, and polygonal cells with high-grade nuclei were observed in 3 cases. Immunohistochemically, 5 cases were entirely immunoreactive for CKpan, whereas 80% HCCC cases were positive for P63, and CK14. None expressed immunoreactivity for S-100, Calponin, or GFAP. The positive rate of Ki-67 staining was about 5% in the classic area of case 3, but 40% in the high-grade area. As for the result of FISH findings, EWSR1 gene break was detected in all 5 HCCC cases. Conclusions Our study has expanded the morphological spectrum of HCCC, and proposed the diagnosis of HCCC should be confirmed by fully analyzing histological, immunohistochemical, and molecular features practically.