Scrape Cytology of DEK::AFF2 Fusion-Associated Papillary Squamous Cell Carcinoma of the Sinonasal Tract Masquerading as Schneiderian Papilloma: A Case Report.

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INTRODUCTION: DEK::AFF2 fusion-associated papillary squamous cell carcinoma is a recently characterized sinonasal neoplasm that closely mimics Schneiderian papilloma. Although one report has described fine-needle aspiration cytology of a metastatic lymph node, scrape cytological features from the primary site remain undocumented. CASE PRESENTATION: We report the scrape cytology of this tumor in a 26-year-old woman. While certain features (perivascular arrangement and intracytoplasmic nuclear debris-like structures) overlapped with Schneiderian papilloma, several findings diverged: a predominantly discohesive pattern, nuclear enlargement with anisonucleosis, prominent nucleoli, stippled chromatin distinct from the neuroendocrine pattern, and a crackled cytoplasmic appearance. Synaptophysin and chromogranin A were negative, excluding neuroendocrine differentiation. CD163 immunohistochemistry confirmed that the debris-containing cells were not histiocytes. E-cadherin showed heterogeneous downregulation in the initial biopsy, suggesting a candidate molecular basis for the discohesive pattern. The diagnosis was confirmed by AFF2 immunohistochemistry, DEK break-apart fluorescence in situ hybridization, and reverse transcription polymerase chain reaction with Sanger sequencing. Retrospective AFF2 immunohistochemistry of the initial biopsy, originally diagnosed as Schneiderian papilloma, was positive. The patient remained free of disease progression at 34 months after completion of chemoradiotherapy for the antecedent lacrimal sac carcinoma. CONCLUSION: These findings provide the first comprehensive cytological documentation of this entity from a primary sinonasal site and delineate features diverging from Schneiderian papilloma that may prompt ancillary investigations.