Malignant Salivary Gland Neoplasm of the Tongue Base with EWSR1::BEND2 Fusion: An Unusual Case with Literature Review.

Purpose: Salivary gland malignancies may have overlapping architectural patterns, tumor morphology, and immunohistochemical phenotypes, presenting challenges in precise classification. Molecular phenotyping has become quite useful for providing an additional diagnostic modality, and potential drug targets. Here we reported a young female patient with salivary gland tumor of the tongue base harboring genetic alterations by next generation sequencing (NGS).

Methods: The morphological, immunohistochemical and molecular features of this case were described, and related literature was reviewed.

Results: The tumor showed an epithelial myoepithelial architecture arranged in cords and tubules interwoven with a chondromyxoid stroma, along with perineural invasion and adjacent striated muscle infiltration. Myoepithelial cells were positive for CK5/6, partially positive for P63 and CK7, and sporadically positive for S100. Immunoprofiling revealed a low density of infiltrating lymphocytes and macrophages and the absence of programmed death ligand 1 (PD-L1). Notably, RNA-based NGS showed EWSR1::BEND2 gene fusion in this tumor, and EWSR1 break-apart was confirmed by fluorescence in situ hybridization. This led to a final diagnosis of a minor salivary gland malignancy with EWSR1::BEND2 fusion. Only two other cases of salivary gland tumors with EWSR1::BEND2 fusion had been previously reported, which were also detected via RNA-based NGS.

Conclusion: This study emphasized that EWSR1::BEND2 fusion may drive the carcinogenesis in salivary glands neoplasia. In clinic RNA-based NGS could be essential for precise genotyping of EWSR1 fusion in this rare disease.