Fig. 1

Histopathologic, immunohistochemical and molecular pathology findings of sinonasal tract and skull base mucoepidermoid carcinoma (MEC). Low-grade MEC consisting of lobules and cysts of epidermoid, mucin, and intermediate cells (A), clear cell variant of MEC with solid lobules of clear cell forming fibrovascular stroma (B), small hyperchromatic nuclei, occasional mucus-producing cells (arrows) (C), neoplastic oncocytic cells showing abundant, finely granular cytoplasm, and a moderate degree of nuclear atypia (D), high-grade MEC showing squamous epithelioid with large nuclei, a few clear mucinous cells (arrows) and intermediate cells (E), bone invasion (F), periodic acid–schiff staining demonstrated the mucus-producing cells (G), diffuse expression of CK7 and intense nuclear staining for p63 in tumor cells (H), FISH revealed MAML2 rearrangement in 7 cases (I)