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Leukaemia cutis in atypical chronic myeloid leukaemia with a t(9;22) (p24;q11.2) leading to <i>BCR‐JAK2</i> fusion
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2008
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A 44-year-old male presented with a violaceous papular scalp rash and bilateral small volume (1 cm) cervical lymphadenopathy. A full blood count showed a mild neutrophil leucocytosis (11.9 × 109/l) and left shift. The blood film was leucoerythroblastic with toxic changes and occasional tear drop poikilocytes. A skin biopsy demonstrated a dense dermal infiltrate comprising intermediate sized blast cells with granular cytoplasm. These cells stained positively with CD117, CD34 and CD43, consistent with granulocytic sarcoma [top left; haematoxylin-eosin stain (H&E)]. A bone marrow aspirate showed features of a myeloproliferative disorder, with granulocytic hyperplasia (1% myeloblasts), large hyperlobulated megakaryocytes and mild dyserythropoiesis. Trephine biopsy sections showed marked hypercellularity with effacement of normal marrow architecture; there was an increase of cells of neutrophilic and eosinophilic lineages, and megakaryocyte clustering with morphologically abnormal forms (top right; H&E). Karyotyping performed on the marrow aspirate revealed 46, XY, t(9;22)(p24;q11.2) in 23 of 50 cells examined (bottom left). Fluorescence in situ hybridization using the BCR/ABL1 dual fusion probe (Vysis) detected no fusion signals and molecular studies for BCR-ABL1 fusion transcripts [expected in association with t(9;22)(q34;q11)] were also negative. Further molecular studies were performed and an abnormal fusion transcript between exon 1 of BCR and exon 17 of JAK2 was amplified and sequenced from the patient’s bone marrow (bottom right). The BCR exon 1 is in-frame with the tyrosine kinase domain of JAK2. This unique BCR-JAK2 fusion gene was clinically manifest as an MPD with early extramedullary transformation. A previous report of an MPD with a BCR-JAK2 fusion (Griesinger et al, 2005) with different breakpoints also showed relatively early blast crisis. Whether BCR-JAK2 positive MPD represents a distinct clinical-pathological entity requires further study.