Fine-needle aspiration cytology of Hodgkin-like ALK-negative anaplastic large cell lymphoma: Cytomorphological clues and the diagnostic value of subtle background cell atypia.

Hodgkin-like ALK-negative anaplastic large cell lymphoma (ALCL) is a morphologically challenging variant that closely resembles classical Hodgkin lymphoma (CHL), particularly in cytological specimens. Fine-needle aspiration (FNA) cytology of Hodgkin-like ALCL has been rarely reported; therefore, detailed cytomorphological analysis is valuable for diagnostic practice and education. We report a rare case of Hodgkin-like ALCL in a 75-year-old Japanese man who presented with a progressively enlarging right axillary mass. Initial FNA cytology revealed scattered large atypical cells with Hodgkin and Reed-Sternberg-like morphology in an inflammatory background, strongly suggesting CHL. However, retrospective review identified subtle yet important diagnostic clues that had initially been overlooked, including nuclear irregularities and atypia in small- to medium-sized background cells, distinctive distribution patterns of atypical cells, and the presence of vascular stromal fragments.Histopathologic examination confirmed ALCL with a characteristic immunophenotype (CD30+, CD15+, PAX5-, Granzyme B+, CD4+, CD25+, EMA+, ALK-). The absence of PAX5 expression was a key discriminator, effectively excluding CHL despite the striking morphological resemblance. This case highlights the diagnostic pitfalls in differentiating Hodgkin-like ALCL from CHL in cytological preparations and emphasizes the importance of systematically evaluating background cellular composition beyond the conspicuous large atypical cells. Careful assessment of nuclear morphology and cell distribution patterns can provide valuable diagnostic clues to prevent misdiagnosis. This rare cytological presentation offers critical educational insights for cytopathologists and underscores the diagnostic value of FNA cytology, particularly when integrated with immunophenotypic analysis and retrospective morphological review in evaluating morphologically challenging lymphoid malignancies.