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Mnemonics, Simplified Concepts & Thoughts

myeloid differentiation aml

Concept of Acute Myeloid Leukemia (AML) FAB Classification

Epomedicine, Aug 23, 2016Mar 10, 2018

Last updated on March 10, 2018

There is no need of mnemonics to remember the FAB classification of Acute Myeloid Leukemia (AML); just remember the process myeloid differentiation. A simple schematic diagram with few intermediate processes and stimulating factors eliminated will meet our purpose here.

myeloid differentiation aml

The cells belonging to the myeloid lineage are:

  1. Granulocytes: Neutrophils, Eosinophils and Basophils
  2. Monocytes and Macrophages
  3. Erythrocytes (RBCs)
  4. Megakaryocytes (Platelets)

In French-American-British (FAB) classification of AML, it is classified from M0 to M7. The scheme takes into account:

  • The degree of maturation (M0 to M3)
  • The lineage of leukemic blast (M4 to M7)
  1. M0 – undifferentiated progenitor cells
  2. M1 to M3 – myelocytes (granulocyte precursors)
  3. M4 to M5 – monocyte precursors
  4. M6 – erythrocyte precursors
  5. M7 – platelet precursors

Simplified FAB classification of AML

  1. M0 – Undifferentiated
  2. M1 – Myeloblastic without maturation
  3. M2 – Myeloblastic with maturation (Commonest type)
  4. M3 – Promyelocytic
  5. M4 – Myelomonocytic (Naegeli type)
  6. M5 – Monocytic (Schilling type)
  7. M6 – Erythroleukemia (Di Gulielmo’s disease)
  8. M7 – Megakaryocytic

AML Concepts in Concise

1. FAB used 30% blasts to delineate chronic myeloid leukemia (CML) from Blast crisis and AML. WHO revised classification uses the presence of ≥20% myeloblasts in the bone marrow or peripheral blood for the diagnosis of AML.

2. Mo, M1 and M2:

  • <3% blasts are MPO positive in M0 and ≥3% blasts are MPO positive in M1
  • <10% maturation beyond myeloblasts = M1
  • >10% mauration beyond myeloblasts = M2
  • Auer rods:
    • M0 – None
    • M1 – 50%
    • M2 – 70%
    • M3 – 100%
  • t(8:21) is pressent in M2

3. M3:

  • Most cases have t(15:17) – results in disruption of Retinoic Acid Receptor (RAR) required for myeloblast maturation.
  • All-trans-retinoic acid is hence, used for treatment of Acute Promyelocytic Leukemia (APL).
  • DIC is seen in 5-10% cases due to prothrombotic release of Auer rods.

4. M4: >20% monocytic precursors (<20% in M2)

  • Myeloperoxidase positive (Myeloblastic) + Auer rod positive (Monoblastic) + Non-specific esterase positive (Monoblastic)

5. M5:

  • >80% monocytic precursors
  • Gum infiltration and hyperplasia
  • High lysozyme level
  • Auer rod negative + Non-specific esterase positive

6. M6:

  • ≥50% erythroid precursors and ≥20% blasts in nonerythroid component
  • Also known as Di Gulielmo’s disease or Syndrome

7. M7:

  • Rapid myelofibrosis due to release of PDGF.
  • Resistant to treatment
  • GATA1 mutations is seen in those associated with Down’s Syndrome.
  • GpIIb/IIIa or vWF positive

8. Ara-C (Cytarabine) is used for the treatment of CML except M3, in which all-trans retinoic acid is used.

9. Remission criteria:

  • Complete remission = Bone marrow blasts <5%, No auer rods
  • Complete blood count recovery = ANC >1000/microlitre and Platelets ≥1,00,000/microlitre
  • Partial remission = ≥50% fall in blasts over pretreatment values

10. M8:

  • There is no M8 in FAB classification, but some authors have proposed rare deno-vo Acute Basophilic Leukemia as M8.
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PGMEE, MRCS, USMLE, MBBS, MD/MS HematologyInternal medicinePathology

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Comments (2)

  1. Surekha Thakur says:
    Jun 5, 2018 at 2:49 pm

    Thanks a lot

    Reply
  2. Dr Premchand Mahajan says:
    Dec 1, 2022 at 10:46 am

    Precisely summarised information.
    Keep it up.

    Reply

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Epomedicine. Concept of Acute Myeloid Leukemia (AML) FAB Classification [Internet]. Epomedicine; 2016 Aug 23 [cited 2025 May 17]. Available from: https://epomedicine.com/medical-students/concept-acute-myeloid-leukemia-aml-fab-classification/.

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