FAB classification

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The FAB classification is a system for the cytomorphological classification of acute leukemia ( acute myeloid leukemia and acute lymphatic leukemia ) and myelodysplastic syndromes . FAB stands for F rench- A merican- B ritish and stems from the fact that in preparing this classification French , American and British hematopathologist were involved. The FAB classification is still used in the clinic for acute myeloid leukemia, but it is increasingly being replaced by the more modern WHO classification, which includes not only cytomorphological, but also genetic and immunological aspects. For acute lymphoblastic leukemia, the classification is now only relevant for the rare L3 subtype.

FAB classification of acute myeloid leukemia

In the first version of the FAB classification from 1976, only types M1 to M6 were included. The FAB types M0 and M7 were added later. The diagnosis of the FAB M0 subtype requires immunocytological methods and is usually made using flow cytometry (testing for the expression of the myeloid markers CD13 , CD33 , CD65 ).

FAB classification of acute myeloid leukemia
FAB subtype designation Morphological characteristics Cytochemistry
(EST = Esterase,
POX = Peroxidase)
Typical cytogenetic aberrations
M0 Acute myeloid leukemia with minimal differentiation Immature blasts with no granulation POX <3%, EST negative -
M1 Acute myeloid leukemia without maturation less than 10% mature cells (= promyelocytes, granulocytes, monocytes), only sparse granulation POX> 3%, EST <20% -
M2 Acute myeloid leukemia with maturation ≥10% mature cells in myelopoiesis, less than 20% monocytes POX> 3% (mostly clearly positive), EST mostly weakly positive t (8; 21) (in approx. 20%)
M2 baso Acute basophil leukemia - t (6; 9)
M3 Acute promyelocyte leukemia 30% promyelocytes (proportion of blasts often less) POX> 3% (mostly strongly positive), EST weakly to moderately positive t (15; 17), rarely t (5; 17), t (11; 17)
M3v Acute promyelocyte leukemia, microgranular form - - t (15; 17)
M4 Acute myelomonocytic leukemia Myeloid cells (blasts + promyelocytes)> 20%, monocytic cells (monoblasts and mature forms) 20% to 80% POX> 3%, EST> 20% -
M4 Eo Acute myelomonocytic leukemia with eosinophilia - - inv (16)
M5 Acute monoblast / monocyte leukemia more than 80% of the myeloid cells are monoblasts or monocytes POX mostly negative to slightly positive, EST> 20% (strongly positive) -
M5a Acute monoblastic leukemia More than 80% of the myeloid cells are monoblasts or monocytes, of which more than 80% are monoblasts or promonocytes POX mostly negative to slightly positive, EST> 20% (strongly positive) -
M5b Acute monocyte leukemia More than 80% of the myeloid cells are monoblasts or monocytes, of which more than 20% are monocytes POX mostly negative to slightly positive, EST> 20% (strongly positive) -
M6 Acute erythroleukemia ( erythremia ) > 50% of all cells are erythroblasts or> 30% of all blasts among the non-erythrocyte cells are erythroblasts, often trilinear dysplasia POX> 3%, EST can be positive -
M7 Acute megakaryoblastic leukemia Highly pleomorphic blasts POX <3%, EST can be positive -

FAB classification of acute lymphoblastic leukemia

FAB classification of acute lymphoblastic leukemia
FAB subtype designation Typical cytogenetic aberrations
L1 acute small cell lymphoblastic leukemia -
L2 acute lymphoblastic leukemia with medium-sized cells -
L3 acute large cell lymphoblastic leukemia t (8; 14), less often t (2; 8), t (8; 22)

FAB classification of myelodysplastic syndromes

FAB classification of myelodysplastic syndromes
FAB subtype Properties of the bone marrow Properties of blood annotation ICD-10 coding
RA (refractory anemia ) <5% blasts ≤ 1% blasts Early stage of MDS. The proportion of immature cells, so-called blasts , is not increased in the bone marrow and is less than 5% of all nucleated cells. D46.0
RARS (refractory anemia with ring sideroblasts ) <5% blasts
> 15% ring sideroblasts
≥1% blasts D46.1
RAEB (refractory anemia with excess blasts) 5-20% blasts <5% blasts RA with proliferation of blasts (5–20% myeloid differentiated blasts). Divided into RAEB-1 (5–9% blasts) and RAEB-2 (10–19% blasts). D46.2

(Incl .: RAEB I and RAEB II)

CMML ( chronic myelomonocytic leukemia ) <20% blasts
increased promonocytes
> 1 × 10 9 / l monocytes
<5% blasts
C93.1-

(Incl.

  • CMML-1
  • CMML-2
  • CMML with eosinophilia
  • C93.10 CMML: Without specification of a complete remission
  • C93.11 CMML: in complete remission)
RAEB-T (RAEB in transformation) 21–30% blasts of
Auer rods
> 5% blasts Precursor to acute myeloid leukemia .

D46.4 Refractory anemia, unspecified

swell

  • Pschyrembel Clinical Dictionary, 257th edition

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