A Case Report of Mucoepidermoid Carcinoma With Extensive Keratinization in Parotid: Expanding the Morphologic Spectrum.

Mucoepidermoid carcinoma (MEC) is the most common malignant tumor of salivary glands in children and young adults. Typically, it is composed of squamoid, mucin-producing and intermediate-types cells. However, overt keratinization is rare. To the best of our knowledge, extensive keratinization or keratin pearls in MEC has never been reported. Keratinization or keratin pearls are regard "practically never seen in low-grade MEC". Herein, we report a case of a 34-year-old woman who presented with a tumor in right parotid gland for 2 months. Microscopically, the tumor was composed of extensive squamous cells with overt keratin pearls, intermediate cells and few scattered mucous cells. MAML2 gene break-apart and CRTC1-MAML2 gene fusion were detected by fluorescence in situ hybridization. This is the first report to describe a MEC case with extensive squamous metaplasia and overt keratin pearls formation, which expands the morphologic spectrum of MEC.