Appearances can be deceptive: acute myeloid leukaemia simulating chronic lymphocytic leukaemia.

OBJECTIVES: To report a rare case of acute myeloid leukemia (AML) with abnormal chromatin clumping (ACC) in myeloblasts mimicking chronic lymphocytic leukemia (CLL), highlighting the associated diagnostic challenges. CASE PRESENTATION: An 82-year-old woman presented with fatigue, weight loss, and pancytopenia. Peripheral blood film revealed 90 % small mononuclear cells with clumped chromatin and basket cells reminiscent of CLL. Flow cytometry of peripheral blood demonstrated a dim CD45-positive blast population negative for B-cell markers (CD19, CD20, CD10) and lacking light-chain restriction. Bone marrow aspiration confirmed hypercellularity with 94 % blasts expressing CD34, CD117, CD123, MPO, and aberrant CD7. Cytogenetic analysis revealed a complex karyotype with 46,XX, 1p36 abnormalities, and next-generation sequencing identified mutations in EZH2, PHF6, WT1, and STAG2. The final diagnosis was AML with myelodysplasia-related mutations (adverse risk, ELN-2022). Despite cytoreductive therapy, the patient showed no response and died within three weeks. CONCLUSIONS: This case highlights the diagnostic challenge posed by AML with ACC, a morphology that can closely resemble CLL. Recognition of this pattern is essential to avoid misclassification, as therapeutic strategies and prognosis differ significantly. Only three similar cases have been reported, underscoring the exceptional rarity and clinical importance of this presentation.