Myelodysplastic Syndrome: Classification & Staging

There are many subtypes of MDS. For each person, the subtype is determined using the results of the blood and bone marrow tests your MDS physician will perform. (Learn about these tests in Diagnosis.)

MDS subtype is determined using either the World Health Organization (WHO) classification system or the French-American-British (FAB) classification system. Both classification systems take into account a number of features of the dysplastic cells, including the number and type of cytopenias (shortages of specific types of blood cells) and the number of blasts in the bone marrow and circulating blood.

Once your physician knows your MDS subtype, he or she can use this information to help select the most-effective treatment, to decide when to start therapy, and to predict the course of the disease.

WHO Classification System

According to the WHO classification system, there are eight subtypes of MDS. The WHO subtypes are distinguished by the percentage of myeloblasts in the bone marrow, the presence of abnormal red blood cell precursors called ringed sideroblasts in the bone marrow, the number of abnormal cell types known as dysplastic lineages in the bone marrow, and the genetic profile of the bone marrow cells.

The characteristics of the eight subtypes of MDS are:

Refractory anemia (RA)

  • anemia (low red blood cell count)
  • no blasts (immature blood cells) or rare blasts in the blood
  • erythroid dysplasia (when the red blood cells in the bone marrow are abnormal in size, shape, and/or number)
  • less than 5 percent blasts in the bone marrow
  • ringed sideroblasts (abnormal red blood cell precursors) comprise less than 15 percent of red blood cells in the bone marrow

Refractory anemia with ringed sideroblasts (RARS)

  • anemia
  • no blasts or rare blasts in the blood
  • erythroid dysplasia
  • less than 5 percent blasts in the bone marrow
  • ringed sideroblasts comprise more than 15 percent of red blood cells in the bone marrow

Refractory cytopenia with multilineage dysplasia (RCMD)

  • low blood counts
  • no blasts or rare blasts in the blood
  • erythroid dysplasia in two or more cell types
  • ringed sideroblasts comprise less than 15 percent of red blood cells in the bone marrow
  • less than 5 percent blasts in the bone marrow

Refractory cytopenia with multilineage dysplasia and ringed sideroblasts (RCMD-RS)

  • low blood counts
  • no blasts or rare blasts in the blood
  • erythroid dysplasia in 10 percent of cells in two or more of the cell types in the bone marrow
  • ringed sideroblasts comprise more than 15 percent of red blood cells in the marrow  
  • less than 5 percent blasts in the bone marrow

Refractory anemia with excess blasts-1 (RAEB-1)

  • low blood counts
  • less than 5 percent blasts in the blood
  • erythroid dysplasia in one or more of the cell types in the bone marrow
  • 5 to 9 percent blasts in the bone marrow

Refractory anemia with excess blasts-2 (RAEB-2)

  • low blood counts
  • up to 19 percent blasts in the blood
  • erythroid dysplasia in one or more of the cell types in the bone marrow
  • 10 to 19 percent blasts in the bone marrow

Myelodysplastic syndrome, unclassified (MDS-U)

  • low blood counts
  • no blasts or rare blasts in the blood
  • erythroid dysplasia in white blood cells or megakaryocytes (the bone marrow cells that make platelets) in the bone marrow
  • less than 5 percent blasts in the bone marrow

MDS associated with isolated del(5q)

  • anemia
  • less than 5 percent blasts in the blood
  • blood platelet levels that are normal or increased
  • normal or increased dysplastic megakaryocytes in the bone marrow
  • less than 5 percent blasts in the bone marrow
  • loss of part of chromosome 5 in the cells in the bone marrow — doctors call this a deletion of “5q,” or on cytogenetic reports it may be referred to as del(5q)

FAB Classification System

The FAB classification system recognizes five main subtypes of myelodysplastic syndromes:

Refractory Anemia (RA)

  • less than 5 percent blasts in the bone marrow; less than 1 percent blasts in the blood
  • low blood counts, most often red blood cells (anemia)
  • normal or hypercellular (increased number of cells) bone marrow

Refractory Anemia with Ringed Sideroblasts (RARS)

  • less than 5 percent blasts in the bone marrow; less than 1 percent blasts in the blood
  • low blood counts, most often red blood cells
  • ringed sideroblasts comprise more than 15 percent of red blood cells in the bone marrow

Refractory Anemia with Excess Blasts (RAEB)

  • 5 to 20 percent blasts in the bone marrow; less than 5 percent blasts in the blood
  • low blood counts, affecting two or more cell types (the red blood cells, white blood cells, or platelets)
  • normal or hypercellular bone marrow

Refractory Anemia with Excess Blasts in Transformation (RAEB-t)

  • 21 to 30 percent blasts in the bone marrow; more than 5 percent blasts in the blood
  • normal or hypercellular bone marrow

Chronic Myelomonocytic Leukemia (CMMoL)

  • 5 to 20 percent blasts in the bone marrow; less than 5 percent blasts in the blood
  • cytopenia of at least two cell lines
  • excessive numbers of monocytes (a type of white blood cell)
  • normal or hypercellular bone marrow

How Can I Learn More about My Prognosis?

In addition to the two classification systems described above, physicians can also get a sense of a patient's prognosis by using the International Prognostic Scoring System (IPSS). This system is based on three factors:

  • percentage of blasts (immature blood cells) in the bone marrow
  • complete blood count results
  • pattern of cytogenetic (genetic) abnormalities

Physicians use this scoring system to determine the extent of each patient's disease, to help determine the best treatment options and when to start treatment, and to determine the prognosis and risk of developing acute leukemia for patients with MDS.

Your MDS physician can confirm your IPSS score once he or she has seen your blood test and bone marrow test results, and can discuss how your IPSS score affects your treatment plan.