Low-Grade Salivary Myoepithelial Carcinoma of the Upper Lip Harboring a Novel CARMN/miR143HG::PLAG1 Fusion.

چکیده اصلی

BACKGROUND: Myoepithelial carcinoma (MECA) represents a rare malignant neoplasm accounting for less than 2% of all salivary tumors, with recurrent PLAG1 rearrangements comprising its predominant underlying molecular aberration. CASE PRESENTATION: A 48-year-old man presented with a 6-month history of a slow-growing, asymptomatic, pink-yellowish, submucosal nodule of the left upper lip measuring approximately 1.2 cm. An excisional biopsy was performed. Histologic examination revealed an infiltrative salivary neoplasm exhibiting a multilobulated growth pattern comprising numerous solid islands, nests, and anastomosing cords of lesional cells. A cribriform-like architecture was focally noted in association with pools of extracellular, amphiphilic, mucinous material. Neoplastic cells demonstrated predominantly epithelioid-to-plasmacytoid and in areas spindled cytomorphology, bland round-to-ovoid nuclei with granular chromatin, occasionally visible nucleoli, and abundant, eosinophilic, often vacuolated cytoplasm. Prominent nuclear pleomorphism and tumor necrosis were not present, while mitotic figures were infrequent (2 per 10 HPFs). Invasion of the adjacent adipose tissue was observed at the periphery of the lesion. The supporting stroma varied from fibrous-to-myxoid and featured mild acute and chronic inflammation. By immunohistochemistry, neoplastic cells were diffusely positive for CK7, SOX10, S100, and calponin, while p40 showed scattered/patchy immunoreactivity. They were negative for mammaglobin. The histomorphologic and immunophenotypic findings supported the diagnosis of low-grade MECA. RNA-based NGS revealed a CARMN/miR143HG::PLAG1 fusion, leading to a chimeric transcript between exons 1-2 of the long non-coding RNA host gene CARMN/miR143HG (chr5q32) and exons 3-5 of PLAG1 (chr8q12.1). CONCLUSION: We report on the clinical, histopathologic and immunophenotypic characteristics of a low-grade MECA of the minor salivary glands with a novel CARMN/miR143HG::PLAG1 fusion, expanding the molecular landscape of salivary myoepithelial neoplasia.

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