The French-American-British (FAB) classification of acute myeloid leukemia (AML) divides myeloid leukemias into different subtypes based on the population of leukemic cells and their cytochemical reactivity.
|
Subtype |
Designation |
Criteria |
|
M0 |
myeloblastic with minimal differentiation |
• >= 30% if ANC Type I blasts • < 3% of blasts are SBB/MP positive • >= 20% of blasts are positive for myeloid associated antigens AND negative for lymphoid antigens |
|
M1 |
myeloblastic without maturation |
• >= 30% of ANC are Type I and Type II blasts • >= 90% of NEC are blasts • >= 3% of blasts are SBB or MP positive |
|
M2 |
myeloblastic with maturation |
• >= 30% of ANC are Type I and Type II blasts • < 90% NEC are blasts • >= 10% of NEC are promyelocytes or more mature granulocytes • < 20% of NEC are of monocytic lineage • usually > 85% of leukemic cells are positive for SBB, MP, and CAE |
|
M3 |
promyelocytic, hypergranular |
• >= 30% of ANC are blasts and abnormal hypergranular promyelocytes • Auer rods and multiple Auer rods • usually > 85% of leukemic cells are positive for SBB, MP, and CAE |
|
M3V |
promyelocytic, microgranular |
• >= 30% of ANC are blasts and abnormal microgranular promyelocytes • hypergranular promyelocytes rare • Auer rods are rare • usually > 85% of leukemic cells are positive for SBB, MP, and CAE |
|
M4 |
myelomonocytic |
• >= 30% of ANC are Type I and Type II blasts • >= 30% myeloblasts, promyelocytes, myelocytes and more mature granulocytes • < 80% NEC are monoblasts, promonocytes or monocytes • > 20% of blasts are positive for SBB, MP, and CAE • > 20% of blasts are positive for NAE, NBE |
|
M4E |
myelomonocytic with eosinophilia |
• same as M4 AND abnormal eosinophilia • eosinophils with large abnormal basophilic granules • eosinophils often CAE positive |
|
M5A |
monocytic, poorly differentiated |
• >= 30% of ANC are blasts • >= 80% NEC are monoblasts, promonocytes or monocytes • >= 80% of monocytic cells are monoblasts • < 20% of blasts are positive for CAE • >= 80% of blasts are positive for NAE, NBE |
|
M5B |
monocytic, differentiated |
• >= 30% of ANC are blasts • >= 80% NEC are monoblasts, promonocytes or monocytes • < 80% of monocytic cells are monoblasts • < 20% of blasts are positive for CAE • >= 80% of blasts are positive for NAE, NBE |
|
M6 |
erythroleukemia |
• >= 50% ANC are erythroblasts • >= 30% of NEC are blasts • many erythroid precursor cells are PAS-positive |
|
M7 |
megakaryoblastic |
• >= 30% of ANC are megakaryoblasts or leukemic cells • leukemic cells are positive for platelet peroxidase or for glycoproteins Ib or IIb/IIIa |
(from Table 27-7, page 679, Davey, 1996)
where:
• Type I blast: no cytoplasmic granules
• Type II blast: small number ( < 20) of primary azurophilic granules
• Type III blast : >= 20 primary azurophilic granules (promyelocytes have a lower nuclear-to-cytoplasmic ratio, more dense nuclear chromatin, and are larger)
• ANC = all nucleated cells
• NEC = non-erythroid cells
• MP = myeloperoxidase
• SBB = Sudan black B
• myeloid cell markers: CD13, CD14 or CD33
• CAE = ASD chloracetate esterase
• NAE = alpha-naphthyl acetate esterase
• NBE = alpha-naphthyl butyrate esterase
• PAS = periodic acid-Schiff
• Auer rods can be found in any of the AML subtypes and in refractory anemia with excess of blasts in transformation; they are especially common in subtypes M1, M2 and M3.
Implementation note:
• I needed to specify percent of abnormal promyelocytes in M3 and M3V to distinguish from M2.
Specialty: Hematology Oncology
ICD-10: ,
