NAB2::STAT6 Rearranged Carcinoma of the Parotid Gland with Sebaceous Differentiation: A Case Report

PURPOSE: The NAB2::STAT6 fusion is predominantly associated with solitary fibrous tumors (SFTs) and is utilized in diagnosing SFTs through nuclear STAT6 protein overexpression. Recent studies expanded the phenotypic spectrum of NAB2::STAT6 rearranged neoplasms, including adamantinoma-like and teratocarcinosarcoma-like phenotypes. We report a case of a NAB2::STAT6 rearranged epithelial tumor exhibiting sebaceous differentiation in the parotid gland.

METHODS: Fine-needle aspiration (FNA), histopathology, immunohistochemistry, and molecular studies of this case were described.

RESULTS: Fine-needle aspiration (FNA) revealed atypical basaloid cells, suggesting primary salivary gland carcinoma or metastasis. Histological examination showed basaloid-squamous cells with a monomorphic appearance containing foci of sebaceous differentiation, expressing pancytokeratin, p40, and androgen receptor, while CD34 staining was negative. Molecular studies identified a NAB2::STAT6 fusion, along with an AKT1 mutation.

CONCLUSION: This case further expands the phenotypic spectrum of NAB2::STAT6 rearranged neoplasms and emphasizes comprehensive histopathological and molecular analysis in challenging head and neck tumors. It suggests STAT6 immunohistochemistry as a potential screening tool for head and neck tumors resembling sebaceous carcinoma, myoepithelial tumors, or GLI1-altered neoplasms.