Chronic Myeloid Neoplasms - Atypical chronic myeloid leukemia (aCML)

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Chronic Myeloid Neoplasms

MDS/MPN

Atypical chronic myeloid leukemia (aCML)

Reviewer: Nikhil Sangle, M.D., University of Utah & ARUP Laboratories (see Reviewers page)
Revised: 3 August 2011, last major update August 2011
Copyright: (c) 2001-2011, PathologyOutlines.com, Inc.

Definition
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● Resembles CML due to increased white blood cell count, primarily neutrophils, >10% neutrophilic precursors, <10% monocytes, splenomegaly common (German National Cancer Institute)
● Differs from CML due to lack of BCR-ABL by cytogenetics or RT-PCR, presence of marked granulocytic and multilineage dysplasia; anemia and thrombocytopenia are common, basophilia is uncommon
● Median age – 7th / 8th decade; male:female 1:1
● Median survival less than 2 years, may progress to bone marrow failure or AML; poor prognosis if age > 65 years, female, low platelets, hemoglobin < 10g/dL, WBC count > 50 x 10⁹/L (Ann Oncol 2000;11:441)

Case reports
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● 83 year old man with leukemic pleural effusion (J Korean Med Sci 2006;21:936)
● 2 year old with t(5;12) successfully treated with imatinib (Leuk Res 2004;28 Suppl 1:S65)

Micro description
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● Peripheral blood: usually <5% blasts; no basophilia / monocytosis; dysgranulopoiesis in the form of pseudo Pelger-Huet or other nuclear abnormality, abnormal cytoplasmic granularity
● Bone marrow: hypercellular marrow with increased M/E ratio, marked granulocytic hyperplasia and dysplasia (convoluted lobulation of nuclei, pseudo-Pelger-Huet forms), <20% blasts
● Variable dyserythropoiesis and dysmegakaryopoiesis
● No/minimal basophilia
● Minimal reticulin fibrosis in some cases

Micro images
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Bone marrow smear: various images

Diagnosis
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● WBC count > 13 x 10⁹/L, no BCR/ABL1 gene fusion, no rearrangement of PDGFRA, PDGRB or FGFR1, >10% neutrophil precursors (promyelocytes, myelocytes, metamyelocytes), basophils <2% of leucocytes, monocytes <10% of leucocytes, blasts <20% of nucleated cells, hypercellular marrow with granulocytic proliferation and dysplasia

Molecular description
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● May have t(8;9) (Cancer Res 2005;65:2662)
● No BCR-ABL rearrangement
● Must use RT-PCR because (a) fusion gene may be present with normal karyotype (Hematol Oncol. 2006;24:86) and (b) karyotype may normalize after imatinib treatment (Leukemia 2004;18:1340)

Molecular images
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PCM1-JAK2 fusion protein in t(8;9)

Differential diagnosis
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● CML: BCR-ABL present, prominent basophils, usually no anemia, no thrombocytopenia, no dysplastic granulocytes

End of Chronic Myeloid Neoplasms > MDS/MPN > Atypical chronic myeloid leukemia (aCML)

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