Types of Myelodysplasia
There are many different types of myelodysplastic syndromes, or MDS. These include:
  • Refractory anemia (RA)
    RA means a shortage of red blood cells that does not respond to conventional anemia treatment. In RA, only a low red cell count is apparent, and both white blood cell and platelet counts are normal. The clinical course of this disease is prolonged, and very rarely transforms into leukemia.
  • Refractory anemia with ringed sideroblasts (RARS)
    RARS is identical to RA, except for the distinction that 15 percent of the red blood cells are abnormal cells called ringed sideroblasts. A sideroblast is a red blood cell that contains iron deposits. As with RA, RARS has a protracted clinical course and rarely progresses to leukemia.
  • Refractory anemia with excess blasts (RAEB)
    In RAEB, myeloblasts account for 5 to 19 percent of the cells in the bone marrow, but the number of blasts in the peripheral blood is normal. There may be changes to the white blood cells and platelets. RAEB may progress to acute myeloid leukemia (AML); the higher the number of blasts, the shorter the clinical course of the disease and the higher the likelihood of transformation to AML.
  • Refractory anemia with excess blasts in transformation (RAEB-t)
    In RAEB-t, in addition to anemia (low red cell count), there is also a shortage of white blood cells and platelets. Here, these shortages are caused by the over-proliferation of blast cells. Some experts don’t even think RAEB-t should exist as a category, and consider it to actually be a form of AML.
  • Refractory cytopenia with multilineage dysplasia (RCMD)
    Here, there is a cytopenia (shortage of cells) of at least two members of the myeloid cell line (which comprises red blood cells, granulocyte-type white blood cells, and platelets) – hence the term “multilineage” – and they are dysplastic, or abnormal. Only a small percentage of RCMD cases progress to AML.
  • Myelodysplastic syndrome associated with an isolated del(5q) chromosome abnormality
    In this MDS, also called “5q-,”patients are anemic, and there is what is known as a deletion abnormality on the “long arm” of chromosome 5 (the short end of a chromosome is called “p” and the long end, “q”). This subtype is associated with a long survival.
  • Unclassifiable myelodysplastic syndrome (MDS-U)
    WITH MDS-U, there is a shortage of at least one type of blood cell, and the number of blasts in both bone marrow and blood is normal. However, it cannot fit into any of the other classifications set forth above for MDS.
  • De novo myelodysplastic syndrome
    The term “de novo” just means “from new” in Latin, meaning the disease just seems to show up out of the blue with no known cause.
  • Secondary myelodysplastic syndrome
    This type of MDS is secondary to (meaning that it occurs as a consequence of) certain environmental factors such as exposure to the following:
    • Tobacco smoke
    • Ionizing radiation
    • Organic chemicals (e.g., benzene, toluene, xylene and chloramphenicol)
    • Heavy metals
    • Herbicides
    • Pesticides
    • Fertilizers
    • Stone and cereal dusts
    • Exhaust gases
    • Nitro-organic explosives
    • Petroleum and diesel derivatives
    • Alkylating agents (often used in cancer chemotherapy)
    • Marrow-damaging agents used in cancer chemotherapy
  • Previously treated myelodysplastic syndrome
    Previously treated MDS are de novo or secondary cases of MDS that have progressed despite previous treatment and, in many cases, are receiving additional treatment.