ALK-Rearranged Epithelioid and Spindle Cell Neoplasm of the Sinonasal Tract.

Anaplastic lymphoma kinase (ALK)-rearranged mesenchymal neoplasms (non-inflammatory myofibroblastic tumor and non-epithelioid fibrous histiocytoma) have been recently described which tend to occur in the superficial and deep soft tissues. Occurrence as a primary sinonasal neoplasm has not been reported thus far. Herein, we describe the first case of sinonasal ALK-rearranged mesenchymal tumor that harbored remarkable epithelioid and spindle cell morphology. The tumor affected a 40-year-old man who presented with flu-like symptoms and was thought to have influenza A. However, computed tomography demonstrated a nasal polypoid lesion causing curvature of the nasal septum. Histological examination revealed a heterogeneous tumor composed of round to epithelioid cells with foci of spindle cells. The tumor cells exhibited moderate pleomorphism and mitotic activity. By immunohistochemistry, they showed diffuse staining of CD34, S100, ALK (D5F3) and CD30. Fluorescence in situ hybridization analysis demonstrated ALK rearrangement. Subsequent next-generation sequencing (RNA-seq) identified a rare PLEKHH2exon6::ALKexon20 fusion. This study further demonstrates the importance of molecular profiling in identifying kinase fusion-positive soft tissue tumors, particularly for those that arise at unusual sites and display atypical cytomorphology.