Sclerosing mucoepidermoid carcinoma (SMEC) of the salivary glands is a rare variant of low-grade mucoepidermoid carcinoma with scanty cellular atypia characterized by marked fibrosis/sclerosis and a rich inflammatory infiltrate. Herein, we report 25 unpublished cases of SMEC, two of them with prominent eosinophilia (2/25; 8%) and three with abundant IgG4-positive plasma cells (3/25; 12%). In our series of salivary SMEC, molecular analysis using fluorescence in situ hybridization (FISH) and/or next-generation sequencing (NGS) provided evidence of MAML2 gene rearrangement in 18 cases of the 21 analyzable cases tested (86%), while this gene locus was intact in 3 cases (14%). This study focuses on the diagnostic criteria of salivary SMEC given its challenge of abundant collagenous stroma, minimal residual neoplastic areas, and inconspicuous mucous cells. Follow-up data of our cases indicate that salivary SMECs have favorable outcomes. Molecular analysis for MAML2 gene rearrangement suggests that SMECs of salivary glands represent a rare variant of conventional low-grade MECs of salivary glands. In contrast, SMECs of the thyroid gland are genetically distinct from salivary-type thyroid MECs.

Bioptic Laboratory Ltd Pilsen Czech Republic

Department of Anatomic Histopathology and Cytogenetics Department of Laboratory Medicine Niguarda Cancer Center Milan Italy

Department of Pathology Antwerp University Hospital University of Antwerp Antwerp Belgium

Department of Pathology Erasmus University Medical Center Rotterdam The Netherlands

Department of Pathology Faculdade de Medicina Instituto Português de Oncologia de Lisboa Francisco Gentil and Institute of Pathology Universidade de Lisboa Lisbon Portugal

Department of Pathology Faculty of Medicine in Pilsen Charles University Pilsen Czech Republic

Department of Pathology Hospital Universitari de Bellvitge Barcelona Spain

Department of Pathology University of Calgary Calgary Alberta Canada

DERMPATH Munich Germany

Institute of Biomedicine Pathology University of Turku and Department of Pathology Turku University Hospital Turku Finland

Institute of Pathology University Hospital Erlangen Friedrich Alexander University Erlangen Nürnberg Erlangen EMN Erlangen Germany

Molecular and Genetic Laboratory Bioptic Laboratory Ltd Pilsen Czech Republic

The Fingerland Department of Pathology Faculty of Medicine Charles University Hradec Králové and University Hospital Hradec Králové Hradec Králové Czech Republic

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