FAB Classification of the Myelodysplastic Syndromes

 

NOTE: This classification has been supplanted by the WHO classification for the myelodysplastic and myelodysplastic-myeloproliferative syndromes (below). A major change in the WHO classification is reduction in blast count from 30% to 20% to define AML.

 

Features of myelodysplastic syndromes:

(1) chronic anemia resistant to treatment with vitamin B12, folate and pyridoxine and showing reticulocytopenia

(2) leukopenia and/or thrombocytopenia may be present

(3) variable abnormalities in monocytes

(4) presence of dyserythropoiesis, dysgranulopoiesis and/or dysmegakaryocytopoiesis

(5) usually a hypercellular bone marrow, but may be hypocellular or feature fibrosis

(6) usually absence of hepatosplenomegaly and lymphadenopathy

 

Dyserythropoiesis:

(1) chronic anemia with reticulocytopenia

(2) ringed sideroblasts

(3) multinucleated red cell precursors

(4) fragmented nuclei in red cell precursors

(5) abnormally low or high numbers of erythroblasts

(6) anisocytosis and poikilocytosis on peripheral blood smear; dimorphic red cell populations may be present

(7) circulating nucleated red blood cells

 

Dysmyelopoiesis:

(1) neutropenia

(2) hypogranular cytoplasm

(3) nuclear abnormalities, including acquired Pelger-Huet anomaly

(4) Auer rods

 

Dysmegakaryocytopoiesis:

(1) thrombocytopenia

(2) increased large platelets without increased consumption

(3) micromegakaryocytes

(4) multiple small nuclei in megakaryocytes

(5) large mononuclear megakaryocytes

 

Subtypes:

(1) refractory anemia (RA)

(2) refractory anemia with ringed sideroblasts (RARS)

(3) refractory anemia with excess of blasts (RAEB)

(4) chronic myelomonocytic leukemia (CMML)

(5) refractory anemia with excess of blasts in transformation to acute leukemia (RAEB-T)

(6) chronic myelomonocytic leukemia in transformation to acute leukemia (CMML-T)

 

Subtype	% bone marrow blasts	% blasts in peripheral blood	Auer rods	Monocyte Count > 1000 /µL	Ring Sideroblasts >15%
RA	< 5%	<= 1%	-	-	-
RARS	< 5%	<= 1%	-	-	+
RAEB	5-19%	< 5%	-	-	+/-
CMML	<=19%	< 5%	-	+	+/-
RAEB-T	20-29% (or)	>= 5% (or)	+/-	+/-	+/-
CMML-T	20-29%	>= 5%	+/-	+	+/-

 

 

Subtype	Median Survival in Months	Leukemic Transformation
RA	50	12
RARS	51	8
RAEB	11	44
CMML	11	14
RAEB-T	5	60
CMML-T