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Leukemia - Acute

AML not otherwise categorized

Acute myeloid leukemia without maturation (FAB AML M1)

Reviewer: Daniela Mihova, M.D. (see Reviewers page)
Revised: 7 February 2013, last major update September 2012
Copyright: (c) 2001-2013, PathologyOutlines.com, Inc.


● 10-20% of AML cases, 44% in one Brazil hospital (Sao Paulo Med J 2006;124:45)
● Usually adults (median age 46 years), present with anemia, thrombocytopenia and neutropenia; may have leukocytosis with markedly increased blasts
● 4% of childhood AML (Orphanet May 2004)

Clinical features

Criteria for diagnosis: 90%+ of nonerythroid cells in marrow are myeloblasts; <10% granulocytic elements; 3%+ of blasts must be positive for myeloperoxidase or Sudan Black B and / or Auer rods by enzyme cytochemistry
Enzyme cytochemistry: 3%+ of blasts are positive for myeloperoxidase or Sudan Black B (confirm by immunohistochemistry if only 3-10% positive for MPO by enzyme cytochemistry); chloroacetate esterase positive
● Poor prognosis

Case reports

● 4 year old child with t(6;9) and basophilia (Ann Biol Clin (Paris) 2003;61:352)
● 44 year old man with large and small blasts (Arch Pathol Lab Med 2004;128:448)
● Presenting with arterial thromboembolism (Leuk Res 2007;31:869)

Micro description

● Typically markedly hypercellular marrow, but normocellular and hypocellular cases occur
● Very immature cells, usually round with few azurophilic cytoplasmic granules or Auer rods
● Nuclei are round or indented; little maturation beyond myeloblast stage
● Cells may may resemble lymphoblasts and not appear myeloid

Micro images

Bone marrow smears (Wright-Giemsa):
Blasts show mild size variation, have pale   Blasts show more variation in size and     Myeloblasts have irregular nuclei with folding and
to slightly basophilic agranular cytoplasm   number of nucleoli, four blasts have     invagination, one myeloblast has numerous
and uniform nuclei with fine chromatin   Auer rods                 azurophilic granules
and prominent nucleoli

Myeloblasts have marked size variation,    Some variation in size, two myeloblasts    Myeloblasts are large with abundant eosinophilic
irregular nuclei with condensed chromatin, have more intense basophilic cytoplasm   cytoplasm, 2 cells have prominent Auer rods, 1
no nucleoli, one blast has a thin Auer rod    and coarse nuclear chromatin        has azurophilic granules and 2 erythroblasts

Agranular myeloblasts have variation in size,
cytoplasmic volume and cytoplasmic basophilia

Bone marrow biopsy:
Marrow is completely replaced by blasts   Biphasic morphology (large and small blasts)
with variable cytoplasm, round/oval nuclei
with mild irregularities and small/indistinct

Peripheral blood smear:

Case with inv(3)(q21q26) shows large and
smaller blasts and normal appearing platelets

Myeloblasts are myeloperoxidase+     Numerous granules are Sudan Black B+   H&E and CD99 (figures B1 & B2)

Flow cytometry description

Clinical Flow Wiki

Positive stains

● Have 1+ myeloid-associated antigens (CD13, CD33, CD117)
● CD34, CD99 and HLA-DR (70%, Mod Pathol 2000;13:452)
● CD7 (30%); CD2, CD4, CD19 and CD56 in 10-20% of cases; rarely CD11b
● Variable CD15, CD71 and HLA-DR

Negative stains

● cCD3, CD14 (usually), CD15, cCD22, CD36 (usually), CD41, CD61, CD64 (usually, Arch Pathol Lab Med 2007;131:748), CD65, cCD79a and glycophorin A

Molecular description

● Associated with t(8;21)
● FLT3 ITD in 22% (Ai Zheng 2007;26:58)
● FLT3 mutations associated with HLA-DR negative patients (Leuk Res 2007;31:921)

Electron microscopy description

● May have heterogeneous features (Ultrastruct Pathol 1995;19:9)

Electron microscopy images

Numerous electron dense granules in Golgi region,
also granules throughout cytoplasm and prominent nucleolus

Differential diagnosis


End of Leukemia - Acute > AML not otherwise categorized > Acute myeloid leukemia without maturation (FAB AML M1)

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