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Leukemia - Acute

AML not otherwise categorized

Acute myeloid leukemia with minimal differentiation (FAB AML M0)


Reviewer: Daniela Mihova, M.D. (see Reviewers page)
Revised: 20 March 2013, last major update September 2012
Copyright: (c) 2001-2013, PathologyOutlines.com, Inc.

General
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● No definitive evidence of myeloid differentiation by morphology and light microscopy cytochemistry; need immunohistochemistry, flow cytometry, or EM cytochemistry to characterize as myeloid
Criteria for diagnosis: nongranular blasts; less than 3% of blasts are positive for myeloperoxidase (MPO), Sudan Black B (SBB) or naphthol-ASD-chloroacetate esterase (CAE) by enzyme cytochemistry, although blasts may express myeloperoxidase by EM or immunohistochemistry; blasts do not express classic lymphocyte antigens, but may aberrantly express some lymphocyte antigens

Clinical features
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● 5% or less of AML cases; any age, mostly infants or older adults
● Typically presents with anemia, thrombocytopenia, neutropenia, marrow failure, but may have leukocytosis with markedly increased blasts
● Children (Blood 2007;109:2314) and adults (Br J Haematol 2001;113:737) may have poorer outcome than other AML subtypes
● Enzyme cytochemistry: negative for nonspecific esterase, although may have non-specific weak or focal reaction distinct from monocytic cells

Case reports
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● 58 year old man with minimally differentiated acute myelogenous leukemia (AML-M0) granulocytic sarcoma in oral cavity (Oral Oncol 2002;38:516)
● Subtelomeric t(5;9)(q35.3;q34.3) and deletion of RB1 gene (Cancer Genet Cytogenet 2008;181:36)
● Deletion of (15)(q11.2q22) (Cancer Genet Cytogenet 2008;184:57)

Micro description
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● Medium sized-blasts, round or slightly indented nuclei with dispersed chromatin
● One or two nucleoli, agranular cytoplasm with varying degree of basophilia and no Auer rods
● Rarely small blasts with condensed chromatin and scant cytoplasm that may resemble lymphoblasts
● Occasionally, residual normal population of maturing neutrophils may be present
● Bone marrow: markedly hypercellular with poorly differentiated blasts

Micro images
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Bone marrow smear (Wright-Giemsa):
   
No differentiated features


M0 (figure A) compared to other AML

Bone marrow biopsy:

Complete replacement of marrow by blasts without differentiation

Stains:
         
Blasts are positive for  CD99          Myeloblasts are negative for myeloperoxidase
myeloperoxidase by IHC              by cytochemistry with positive staining in neutrophil

Flow cytometry description
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● Pediatric AML-M0 is usually CD33 bright, TdT-, CD34- and CD13-/weak (Am J Clin Pathol 2000;113:193, Clinical Flow Wiki)

Flow cytometry images
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Various gating plots

Positive stains
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● CD13, CD33 (Am J Clin Pathol 2001;115:876), CD34, CD117 (Am J Clin Pathol 2002;117:380), HLA-DR and CD38
● Variable expression of myeloperoxidase, Sudan Black B, TdT (50%), CD2, CD4, CD7 (40%) and CD16 / CD56

Negative stains
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● CD11b (usually), CD14 (usually), CD15 (usually), CD36 (usually), CD41, CD61, CD64 (usually, Arch Pathol Lab Med 2007;131:748) and most lymphocyte antigens(CD5, cCD3, cCD79a, cCD22)
● Glycophorin A

Molecular description
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● Often complex chromosomal abnormalities; tend to have more -5/del(5q), -7/del(7q), +8 and del(11q), but these should be reclassified as AML-MRC
● AML1 / CBFA / RUNX1 (27%) and strong association with trisomy 13 and FLT3 mutation (16-22%, Haematologica 2007;92:1123)
● More often trisomy 21 and hypodiploidy than other AML, although outcome is similar (Blood 2007;109:2314)

Electron microscopy description
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● Resembles myeloblasts; may show focal myeloperoxidase+ granules

Electron microscopy images
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Granules are myeloperoxidase positive

Differential diagnosis
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● Acute leukemia of ambiguous lineage
ALL
● AML-MRC
Mixed phenotypic leukemia
AML-M7 (megakaryoblastic)
● Leukemic phase of large cell lymphoma

End of Leukemia - Acute > AML not otherwise categorized > Acute myeloid leukemia with minimal differentiation (FAB AML M0)


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