OVERVIEW
Myelodysplastic syndrome (MDS) is a syndrome consisting of a group of disorders that are related to each other, due to the fact that the boundaries between the individual disorders are sometimes unclear and that the disorders can progressively transform from one to another. The prognosis of each type is different, at least in the short term, and typing is therefore important.
Typing criteria
1.FAB typing
In the 1970s to 1980s, a collaborative group of hematologists from France, the United States and the United Kingdom (referred to as FAB) retrospectively summarized a large number of cases, described the characteristics of MDS in detail, and put forward diagnostic criteria and typing suggestions, which have been accepted by scholars around the world after decades of application.
The FAB collaborative group classifies MDS into five subtypes, and the main basis for typing is the proportion of primitive cells in the bone marrow and peripheral blood, as well as the percentage of ringed iron granulocytes in the bone marrow and the absolute value of monocytes in the peripheral blood. The typing criteria are as follows:
(1) Refractory anemia, abbreviated as RA, has <5% of primitive cells in the bone marrow and <1% of primitive cells in the peripheral blood.
(2) Refractory anemia with excess of primitive cells, abbreviated as RAEB, with bone marrow primitive cells of 5% to 20% and peripheral blood primitive cells of <5%.
(3) Refractory anemia with excess of primitive cells in transformation, abbreviated as RAEBT, with 21% to 30% of primitive cells in the bone marrow and ≥5% of primitive cells in the peripheral blood.
(4) Refractory anemia with ringed iron granulocytes, abbreviated as RAS, the proportion of primitive cells in bone marrow and peripheral blood is the same as that of RA, and ringed iron granulocytes account for more than 15% of the nucleated erythrocytes after iron staining of bone marrow.
(5) Chronic granulomonocytic leukemia, abbreviated as CMML, has the same proportion of primitive cells in the bone marrow and peripheral blood as RAEB, and the absolute value of peripheral blood mononuclear cells is more than 1×109/L.
2. WHO typing
(1) Revision of FAB typing Although the FAB typing of MDS is widely recognized, there are still many problems and even controversies in practice, therefore, the World Health Organization (WHO) revised the FAB typing in 1997 and recommended it as the international standard. The main points of its revision are as follows:
(1) Emphasize that RA and RAS can be diagnosed only if there are abnormalities in the development of erythrocyte lineage blood cells, whereas the original FAB criteria require at least two lineages of blood cells to be abnormal for diagnosis.
(2) Two new subtypes have been added, one is refractory cytopenia with multilineage dysplasia, abbreviated as RCMD, which actually has the same number of primitive cells in bone marrow and peripheral blood as RA, but emphasizes that the abnormalities of hematopoiesis are related to at least two lines of hematopoiesis. The second is the 5q-syndrome, in which chromosomal examination reveals a deletion of the long arm of chromosome 5, and the bone marrow and peripheral blood features are basically the same as those of RA, except that the abnormalities of the megakaryocyte lineage are more prominent (a marked increase in small megakaryocytes in the lobular decrease). Clinically, it is mainly seen in elderly women. The peripheral blood leukocyte count is only mildly reduced or normal, while the platelet count is often normal or increased, but the anemia is very prominent, and the survival time is relatively long, as long as the regular blood transfusion can be survived for more than 7 years, and it rarely transforms into acute leukemia.
(3) The cut-off value for the percentage of primitive cells in the bone marrow for diagnosing AML and MDS has been reduced from 30% to 20%, i.e., AML is diagnosed when the number of primitive cells in the bone marrow reaches 20%, thus eliminating the RAEBT subtype in the FAB typing.
(4) CMML in the FAB typing was categorized under myeloproliferative diseases, i.e., CMML is no longer a subtype of MDS.
(5) The RAEB in the original FAB typing is subdivided into two types: RAEB-I has relatively fewer primitive cells in the peripheral blood and bone marrow, <5% and <10%, respectively; and RAEB-II has 5%-19% and 11%-19%, respectively, i.e., there are more primitive cells than in RAEB Ⅰ.
(6) Finally, another subtype is added, which is called MDS untypable, and refers to the patient who has numerous features of MDS in laboratory tests, but it is difficult to be categorized into any subtype.
(2) WHO’s MDS typing
1) Refractory anemia (RA).
2) Refractory anemia with ringed iron granulocytes (RAS).
3) Refractory hemocytopenia with multilineage dysplasia (RCMD).
4) Refractory anemia with excess of primitive cells type I and II (RAEB-I, RAEB-II).
5) 5q-syndrome.
6) Myelodysplastic syndromes that cannot be typed (MDS, cannot be typed).
Trends
Since WHO typing is proposed, hematologists from various countries still have different opinions about it and have raised some questions, so it has not been unanimously recognized and widely used. At present, most of the scholars in China still follow the FAB typing, but it is possible to replace the FAB typing after WHO typing is further amended.