Myelodysplastic syndromes (MDS) are a group of closely related diseases that arise in the bone marrow due to a disorder of the hematopoietic stem cells, the immature cells from which all blood cells develop. As a result, the bone marrow makes reduced numbers of red blood cells (which carry oxygen), white blood cells (which fight infection), or platelets (which prevent or stop bleeding), or any combination of the three. In addition, the cells in the blood and bone marrow (also called myelo) usually look abnormal (or dysplastic), hence the name myelodysplastic syndromes.
Each year between 15,000 and 20,000 new cases of MDS are diagnosed in the United States. Patients tend to be around the age of 70 at the time of diagnosis, although people of any age can develop the disease. MDS is classified as either primary (also called de novo) — disease that has no known cause — or secondary (also called treatment-related) MDS.
Treatment-related MDS is caused by previous treatment with chemotherapy or radiation therapy, which is given for a previously diagnosed cancer. In the United States, the number of new cases of MDS is rising, both because older people make up a growing segment of the population and because people now live longer after treatment for their first cancer.
In the past, MDS was commonly referred to as a preleukemic condition (and it is still sometimes called preleukemia) because some people with MDS develop acute leukemia as a complication of the disease. However, most patients with MDS will never develop acute leukemia.
How MDS Develops
Hematopoietic stem cells are produced in the bone marrow, where they mature (or differentiate) into functioning blood cells. MDS arises when one of these stem cells transforms from a normal cell into a malignant cell, one capable of uncontrolled proliferation. The malignant cell begins producing identical copies, or clones, sometimes referred to as dysplastic clones. These clones may be unable to make blood cells efficiently, or the blood cells that are produced may die prematurely.
As a result, blood counts are usually low in people with MDS. As the number of healthy cells declines in a patient’s body, he or she may be prone to anemia (a lack of oxygen-carrying red blood cells), infections caused by low numbers of infection-fighting white blood cells, as well as bruising and bleeding, resulting from low levels of platelets. In addition, the presence of abnormal blood cells can increase the likelihood of bleeding and infections.
Over time, very immature bone marrow cells called blasts may increase in number and fill the bone marrow, displacing the normal red and white blood cells and platelets that are produced there. This overgrowth of blasts, if severe enough, is called acute leukemia.
Myelodysplastic syndrome has a few known risk factors:
- People who have received previous chemotherapy or radiation treatment for cancer have an increased risk of developing MDS, because chemotherapeutic agents and radiation therapy can cause damage to the stem cells in the bone marrow. When chemotherapeutic drugs are combined with radiation therapy, a patient’s level of risk of developing MDS and leukemia is heightened.
- People who are exposed to high levels of benzene or radiation over long periods of time are also at greater risk of developing MDS.
The majority of people who develop MDS have no identifiable risk factors. Scientists do know that many cases of MDS are associated with specific changes in the DNA (genetic material) of the bone marrow cells, but in most cases it is not clear what causes those changes. There are a number of types of MDS, and so it is likely that there are many different underlying causes of MDS.
Symptoms of myelodysplastic syndromes include any of the following:
- Headache, lightheadedness, shortness of breath, paleness, and fatigue, all of which result from anemia
- Susceptibility to infections, especially in the lungs, throat, sinuses, and skin, as well as mouth or ear infections or periodontal disease, which can result from neutropenia (a shortage of a specific type of white blood cell called a neutrophil)
- Bruising, nosebleeds, and pinpoint red spots or rashes on the skin from thrombocytopenia (a shortage of blood platelets)