Classification of AML

WHO classification of AML defines that 20% blasts are required for the diagnosis of AML. In addition, patients with clonal cytogenetic abnormalities t(8;21)(q22;q22), inv(16)(p13q22) or t(16;16)(p13;q22) and t(15;17)(q22;q12) are considered to have AML regardless of the blast percentage.

FAB classification of AML:

• Type M0—acute undifferentiated leukemia

• Type M1—myeloblastic leukemia without maturation; morphologically indistinguishable from L2 morphology (Table 14-3)

• Type M2—myeloblastic leukemia with differentiation

• Type M3—acute promyelocytic leukemia (APML); most cells abnormal hyper-granular promyelocytes; cytoplasm contains multiple Auer rods

• Type M3V—microgranular variant of APML; cells with deeply notched nucleus; typical hypergranular promyelocytes less frequent (see page 441)

• Type M4—both myelocytic and monocytic differentiation present in varying proportions

• Type M4EOS—associated with prominent proliferation of eosinophils

• Type M5—monocytic leukemia containing poorly differentiated and/or well-differentiated monocytoid cells (The M4 and M5 subtypes are particularly common in children under 2 years of age.)

• Type M6—erythroleukemia (Diguglielmo disease)

• Type M7—megakaryoblastic leukemia; associated with myelofibrosis; frequently observed in children with trisomy 21.

M7 Leukemia

1. Blast morphology: In M7 the blast morphology is heterogeneous in appearance, resembling L1 or L2 cells with or without granules and having one to three nucleoli; the cytoplasm has blebs.

2. Immunophenotype: CD41, CD42, CD61 positivity, in addition to CD13 and CD33 positivity.

3. Electron microscopy:

a. Demonstration of platelet peroxidase (PPO)

b. Positive PPO reaction localized exclusively on the nuclear membrane and the endoplasmic reticulum.

FAB M5 and M7 are more common in early childhood, whereas older children are more likely to have M0, M1, M2, and M3.

The quantitative bone marrow criteria for the diagnosis of acute myeloblastic leukemia are summarized in Table 14-17.

Uncommon subtypes of AML leukemia:

1. AML with erythrophagocytosis—M4 or M5 morphology with prominent eryth-rophagocytosis; fibrinolysis and consistent karyotype t(8;16)(p11;p13); associated with a poor prognosis.

2. M0—Lymphoblastic (L2) morphology; negative myeloperoxidase (MPO) and Sudan black by conventional histochemical methods, despite the positivity for myeloid antigens (CD13 and/or CD33). MPO detected by the monoclonal antibody method (which detects the a-chain as well as the inactive proenzyme form) or by electron microscopy may be positive. Lymphoid markers other than TdT and CD7 are negative.

3. M3V-microgranular variant of acute promyelocytic leukemia (APML)—M3V is characterized by bilobed cells, multilobular cells, or cells with reniform nucleus and cytoplasm with minimal or no granulation; generally associated with a few typical M3 cells. It presents with hyperleukocytosis and severe coagulopathy. Prognosis is poor as a result of fatal hemorrhages in vital organs during induction therapy. It displays the same cytochemical (MPO+), cytogenetic t(15;17), phenotypic (HLA-DR, CD13+, CD15+, CD33+), and molecular (RAR and PML rearrangements) features as the hypergranular (M3) APML. Morphologic diagnosis can be difficult.

Table 14-17. Quantitative Bone Marrow Criteria for the Diagnosis of Acute

Myeloblastic Leukemia Subtypes"

Table 14-17. Quantitative Bone Marrow Criteria for the Diagnosis of Acute

Myeloblastic Leukemia Subtypes"

Bone marrow cells

Ml (%)

M2 (%)

M4 (%)

M5 (%)

M6 (%)


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  • awet
    WHO classification of AML 2012?
    8 years ago

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