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

Abstract

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.

Keywords: BEND2; EWSR1; Minor salivary gland carcinoma; Next-generation sequencing.

Fig. 1

Maxillofacial and neck magnetic resonance imaging A–B. Transverse and coronal T2-weighted postgadolinium MR images revealed a heterogeneous linear sheet-enhancing mass with distinct peripheral ring enhancement at the right base of the tongue, measuring approximately 2.5 cm × 1.7 cm × 2.0 cm. C. Sagittal T1-weighted postgadolinium MR image demonstrating that the lesion was adjacent to the lower border of the right palatine tonsil and slightly compressed the oropharyngeal epiglottis

Fig. 2

H&E staining of expectorate and needle puncture biopsy tissue. H&E staininh of the expectorate: A-B. The expectorate showed a polypoid growth pattern with mild atypia squamous epithelium and high cellularity stroma (40 × , 100 ×); C. The cells melted into the chondromyxoid stroma under the epithelium (200 ×). H&E staining of core needle puncture biopsy tissue: D–E. The tumor cells exhibited an invasive growth pattern (40 × ,100 ×); F. Bilayer tubular, cord and solid structures were present (100 ×)

Fig. 3

H&E staining of the surgical resection specimen. A–B. The complicated growth pattern in the surgical specimen (20 ×). C-D. The tumor cells were arranged in a solid and cribriform pattern (40 ×). E–F. Mucous cells and the intermediate cells with a reduced cytoplasm were observed (100 ×). G–H. Myoepithelial cells melting with the stroma (200 ×)

Fig. 4

IHC staining. A–B. CK5/6 and P63 staining revealed the myoepithelial component in the tumor (100 × , 40 ×). C. CK7 staining revealed the ductal component in the tumor (40 ×). D. Negative S100 staining (100 ×). E. Low Ki-67 staining (approximately 10% positive) (100 ×). F. Positive AB staining in mucocytes (100 ×)

Fig. 5

Intratumoral tumor-infiltrating lymphocytes expression of IHC. A–B. The scarce positive for Intratumoral CD4 and CD8(100 ×). C. Negative CD80 staining(100 ×). D. Low level of intratumoral CD68-positive TILs (approximately 5%) (100 ×). E. Low level of intratumoral CD68-positive TILs (approximately 5%) (200 ×) F. Negative PD-L1 staining(100 ×)

Fig. 6

RNA sequencing of EWSR1::BEND2 and GNAQ(intergenic)-EWSR1 fusions. A. RNA-based NGS revealed that EWSR1 was fused with BEND2 as the 3’ partner, an in-frame fusion of EWSR1 exon 8 with BEND2 exon 2 (Transcript accession: NM_013986.3/NM_153346.4. Breakpoint: chr22:29,683,123, chrX:18,234,853). B. RNA-based NGS revealed that a reading frame unclear fusion of GNAQ intergenic with EWSR1 exon 10 (Transcript accession: NM_002072.3/NM_013986.3. Breakpoint: chr9:80,333,072, chr22:29,686,054). C. FISH showed EWSR1 fused signal (yellow), and split signal (red and green). D. MAML2 FISH testing was negative