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Acute mast cell leukemia: A rare but highly aggressive hematopoietic neoplasm

A 18-year-old lady was admitted in our hospital for a 3 month-history of lower back pain, weight loss and severe fatigue. Clinical examination showed hepatosplenomegaly and mild ecchymosis. Her laboratory investigations revealed anemia (hemoglobin 6.6 g/dL), thrombocytopenia (82 3 10/L), and eosinophilia (4.5 3 10/L). Meticulous blood smear examination showed the presence of few circulating atypical mast cells (MCs) (not appearing on the final leukocyte count). Bone marrow aspiration revealed a massive infiltration (>70% of all nucleated cells) by a morphologically heterogeneous MCs population (Figure 1A). Indeed, while some MCs were heavily granulated with a unique nucleus, others presented with major atypia (bior multi-nucleated cells and/or abnormal distribution of cytoplasmic granulations). Of note, numerous hemophagocytic mast cells (a finding frequently reported in mast cell leukemia [MCL]) were observed (Figure 1B). The hemophagocytic syndrome could not be biologically confirmed because the patient refused additional blood tests. Flow cytometric analysis on bone marrow revealed that the neoplastic cells expressed CD203c, CD117, CD30, CD25 but not CD2 (Figure 2). immunohistochemical staining confirmed positivity for tryptase, CD30 and CD117 in the malignant MCs (Figure 3). These findings were