The First Report of Cytology of DEK::AFF2 Fusion-Associated Papillary Squamous Cell Carcinoma on Fine-Needle Aspiration.

DEK::AFF2 fusion-associated papillary squamous cell carcinoma is a recently characterized sinonasal malignancy defined by its unique translocation. DEK::AFF2 carcinomas may be deceptively monotonous and lack keratinization, resembling transitional epithelium. The lack of traditional cytological atypia presents diagnostic challenges. Our case describes the first report of fine-needle aspiration cytology of a lymph node involved by DEK::AFF2 carcinoma in a patient with previously resected sinonasal inverted papilloma with carcinomatous transformation six years prior to presentation. This aspirate consisted of a lymphoid-rich background admixed with a moderate amount of epithelial cells arranged in cohesive structures of variable size, including large sheets. The tumor cells resembled those of the corresponding biopsy, featuring mildly hyperchromatic nuclei with fine to vesicular chromatin. Lesional cells lacked keratinization, mitoses, or hyperchromasia. Our finding suggests that in nodal aspirates of patients with a history of sinonasal-type papillomas, especially those with prior malignant transformation or atypia, there should be consideration for the possibility of DEK::AFF2-related primary. When in doubt, DEK FISH of AFF2 immunohistochemistry should be performed for confirmation.