Bone marrow neoplastic

Bone marrow - neoplastic myeloid

AML not otherwise specified

AML without maturation (FAB AML M1)

Topic Completed: 1 February 2013

Minor changes: 10 December 2021

Copyright: 2001-2022,, Inc.

PubMed Search: Acute myeloid leukemia [title] without maturation FAB AML M1

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Cite this page: Mihova D. AML without maturation (FAB AML M1). website. Accessed January 28th, 2022.
Definition / general
  • 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
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
Microscopic (histologic) 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
Microscopic (histologic) images

Bone marrow smears (Wright-Giemsa):
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Blasts show mild size variation, have pale
to slightly basophilic agranular cytoplasm
and uniform nuclei with fine chromatin
and prominent nucleoli

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Blasts show more variation in size and
number of nucleoli, four blasts have
Auer rods

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Myeloblasts have irregular nuclei with folding and
invagination, one myeloblast has numerous
azurophilic granules

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Myeloblasts have marked size variation,
irregular nuclei with condensed chromatin,
no nucleoli, one blast has a thin Auer rod

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Some variation in size, two myeloblasts
have more intense basophilic cytoplasm
and coarse nuclear chromatin

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Myeloblasts are large with abundant eosinophilic
cytoplasm, 2 cells have prominent Auer rods, 1
has azurophilic granules and 2 erythroblasts

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

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

Peripheral blood smear:
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Case with inv(3)(q21q26) shows large and
smaller blasts and normal appearing platelets

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Myeloblasts are myeloperoxidase+

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Numerous granules are Sudan Black B+

Positive stains
Negative stains
Molecular / cytogenetics description
Electron microscopy description
Electron microscopy images
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Numerous electron dense granules in Golgi region,
also granules throughout cytoplasm and prominent nucleolus

Differential diagnosis
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