Fine‐Needle Aspiration Cytology of Gingival Acute Promyelocytic Leukemia: Cytomorphologic Clues to an Unusual Extramedullary Presentation

ABSTRACT Introduction Acute promyelocytic leukemia (APL) is a hematologic emergency in which prompt diagnosis is essential to reduce early hemorrhagic mortality. Although oral manifestations are well recognized in acute myeloid leukemia, gingival infiltration is distinctly uncommon in APL, and concomitant central nervous system (CNS) involvement at presentation is exceptionally rare. As gingival lesions may be sampled during their diagnostic evaluation, recognition of characteristic cytomorphology on fine‐needle aspiration cytology (FNAC) can provide an early clue to the underlying hematologic malignancy. Case A 30‐year‐old man presented with excessive post‐tooth‐extraction bleeding, diffuse gingival enlargement, and left facial palsy. FNAC of the gingival swelling demonstrated scattered abnormal hypergranular promyelocytes with folded nuclei, multiple Auer rods, and occasional faggot cells in a hemorrhagic background, strongly suggestive of APL. Subsequent peripheral blood flow cytometry, bone marrow examination, and molecular testing confirmed PML::RARA ‐positive APL. Cerebrospinal fluid cytology and flow cytometry established concurrent CNS involvement. Treatment with all‐trans retinoic acid and arsenic trioxide resulted in hematologic remission and complete resolution of the gingival enlargement. Conclusions This case highlights the diagnostic value of gingival FNAC in the rapid identification of uncommon extramedullary presentations of APL. Knowledge of the characteristic cytomorphologic features facilitates early diagnosis and timely initiation of the life‐saving differentiation therapy.