Nonsebaceous Lymphadenoma-like Mucoepidermoid Carcinoma: A Rare Case Report

Nonsebaceous lymphadenoma-like mucoepidermoid carcinoma (NSLA-like MEC) is an exceedingly rare subtype of MEC. We present such a tumor in a 65-year-old woman with a 2-year history of a left parotid mass. Histologically, the tumor was characterized by a proliferation of neoplastic epithelial cells within a prominent lymphoid stroma containing germinal centers. The epithelial component displayed a bilayered or multitiered growth pattern composed of inner cuboidal cells and outer basaloid cells, forming tubules, microcysts, and complex glandular and cribriform structures. Immunohistochemically, the outer basaloid cells were positive for P63 but were negative for S100 and SMA, while the inner cuboidal cells were positive for keratin 7. Mucicarmine stain demonstrated intracytoplasmic mucin in a small percentage (<1%) of epithelial cells. Fluorescence <i>in situ</i> hybridization analysis revealed <i>CRTC1::MAML2</i> fusion in 78% of tumor cells, confirming the diagnosis of MEC. The morphological distinction between NSLA-like MEC and NSLA poses a significant diagnostic challenge. Features suggestive of MEC include complex branched glandular structures and subtle cytologic atypia. We emphasize the importance of incorporating <i>MAML2</i> molecular testing into diagnostic algorithms for accurate classification, particularly in challenging lesions with lymphoid-rich stroma.