Myelodysplastic Syndrome (MDS)

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Myelodysplastic Syndrome Facts

Myelodysplastic syndrome (MDS) is not a single disease but a group of diseases that affect blood cell formation. In all forms of MDS, a bone marrow problem leads to low levels of blood cells circulating in the blood. “Myelo” refers to bone marrow, which is the body’s blood-cell factory. “Dysplastic” refers to abnormal growth or development. “Myelodysplastic,” therefore, refers to the fact that the bone marrow produces abnormal blood cells.

Each year about 15,000 to 20,000 people are diagnosed with MDS in the United States. At Seattle Cancer Care Alliance, we see about 200 patients every year who have MDS or related diseases.

Healthy Blood Cell Formation 

In a healthy body, the stem cells in the bone marrow generate daughter cells that go through stages of development within the marrow and eventually mature into cells that circulate in the blood: red blood cells (RBCs), white blood cells (WBCs), and platelets. These are the cells that perform their various important functions throughout the body:

  • RBCs carry oxygen throughout the body
  • WBCs fight infection
  • Platelets protect against easy bleeding by helping your blood to clot

Blood Cell Formation in MDS

In MDS, blood stem cells don’t function normally. Instead of making healthy RBCs, WBCs or platelets, and releasing them into the blood stream, the stem cells mature abnormally. They tend to remain at an immature stage and to die prematurely, even before getting out of the marrow.  So most patients with MDS (80 to 85 percent) have more cells in their marrow than do healthy people (this is called hypercellular marrow), but the cells do not live to make it into the blood or they do not stay in circulation long. This is why patients with MDS have cytopenia, or low levels of one or more types of blood cells in their circulation.

  • A low level of RBCs is called anemia. 
  • A low level of WBCs is called neutropenia. 
  • A low level of platelets is called thrombocytopenia.

Low levels of blood cells, or low blood cell counts, cause the symptoms of MDS.

MDS Progression 

MDS progresses in one of two ways over time:

  • In most patients, fewer and fewer healthy blood cells are produced or survive. This can lead to severe anemia (low RBCs), increased risk of infection (due to low WBCs), or risk of severe bleeding (due to low platelets).
  • In about 30 percent of patients, the number of very immature abnormal cells in the marrow, called “blast cells” or “blasts,” increases, and MDS transforms into acute leukemia, [LINK TO leukemia page] a cancer of the marrow and blood. This is why MDS is also referred to as “preleukemia” or “smoldering leukemia.

Subtypes of MDS

Doctors divide MDS into subtypes depending on:

  • Whether you have increased numbers of blast cells in your bone marrow (or  blood), and what percentage of your blood or marrow is made up of these blasts
  • Whether the marrow shows dysplasia in only one type of blood cell (unilineage dysplasia) or in more than one type of blood cell (multilineage dysplasia)
  • Whether there are chromosome abnormalities in the marrow cells and, if so, which type or types of abnormalities
  • Doctors also look at the surface markers of MDS cells to see whether the cells express certain antigens. Antigens are substances (often proteins) that are recognized by the immune system.
  • These and additional factors (in particular, other health problems) may help your doctor decide which treatment options make the most sense for you and how aggressive your treatment should be.

Here is a list of MDS subtypes, according to the World Health Organization (WHO) system of MDS classification:

  • Refractory anemia (RA). This subtype means that you have too few RBCs in your blood (you have anemia), and the marrow shows “dysplastic” cells only among those that make RBCs. Your RBC and platelet counts may be normal.
  • Refractory anemia with ring sideroblasts (RARS). Ring sideroblasts are early stages of RBCs that have accumulated abnormal amounts of iron, which shows up as a ring when stained with a particular dye. This subtype typically means that you have too few RBCs in your blood (you have anemia). Your WBC and platelet counts may be normal.
  • Refractory cytopenia with multilineage dysplasia (RCMD). This subtype means that your marrow shows “dysplastic” changes not only in the cells making RBCs but also in those making WBCs or platelets (or both). You usually have too few cells of at least one cell type in your blood. You also have a low percentage of blasts in your marrow and blood. If a person has multilineage dysplasia and ring sideroblasts, this is classified as RCMD-RS. 
  • Refractory anemia with excess blasts 1 (RAEB1) and refractory anemia with excess blasts 2 (RAEB2). These subtypes mean that you have at least 5% or at least 10 percent but less than 20% blasts in your marrow. 
  • MDS associated with isolated abnormality of chromosome 5 [del(5q)]. This subtype means that part of chromosome #5 is missing. You typically have too few RBCs in your blood (you have anemia). You have a low percentage of blasts in your marrow and blood.
  • MDS unclassified (MDS-U). This subtype means that your marrow shows “dysplastic” cells among those that make WBC or platelets (but not among those that make RBCs) You have a normal percentage of blasts in your marrow and blood. And your MDS does not fit into one of the other subtypes.
  • View details of the WHO classification system.

Symptoms, Diagnosis, & Risks

Here is information on the symptoms, diagnosis, and risks for MDS.

Prognosis & Staging

Here is information on the prognosis and staging of myelodysplastic syndrome.