Two benign adenomatous lesions are commonly recognized within the sinonasal tract, namely respiratory epithelial adenomatoid hamartoma (REAH) and seromucinous hamartoma (SH). We present 10 hitherto unrecognized benign polypoid nasal and sinonasal tumoriform lesions having in average 3.6 cm in largest dimension, which are histogenetically related to SH and REAH. In addition to typical structures of REAH and SH, these lesions contained an additional characteristic and slightly atypical adenomatous component, which we termed atypical sinonasal glands arising in SH (ASGSH). ASGSH often produced deep red colored secretion with peripheral clearing similar to that seen in thyroid follicles. In contrast to SH, ASGSH was endowed by both secretory and myoepithelial layers and had mostly angulated shapes with snout-like protrusions into the lumens. Both layers were formed by an irregular, disorganized, and often incomplete cell lining, which had slightly atypical cytological features without mitoses. In 3 cases, ASGSHs revealed sebaceous differentiation, and in 3 cases the stroma produced a well-differentiated cartilage. Neoplastic nature of ASGSH was supported by finding of various mutations as revealed by next generation sequencing in five cases. In two cases each, we found identical mutations in BRAF gene (Val600Glu), and RET gene (Arg912Trp), respectively and in one case FAT1 gene alteration (Pro1665Leu).

Bioptic Laboratory Ltd Plzen Czech Republic

Cytopathos Ltd Bratislava Slovak Republic

Department of Pathology and Laboratory Medicine University of Calgary Calgary Canada

Department of Pathology and Molecular Pathology University Hospital and University of Zurich Zurich Switzerland

Institute of Pathology Friedrich Alexander University of Erlangen Nuremberg University Hospital of Erlangen Erlangen Germany

Sikl's Department of Pathology Faculty of Medicine in Plzen Charles University and University Hospital E Benese 13 305 99 Pilsen Plzen Czech Republic

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

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