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Myelodysplastic syndromes (MDS) are a group of diseases that affect the bone marrow and blood. In MDS, the blood-forming cells in the marrow slow down, or even stop, making the three types of blood cells. Most patients with MDS will develop anemia (low numbers of red blood cells) and may need blood transfusions. Some patients also have low numbers of white blood cells (which fight infections) and platelets (which help blood clot when you bruise or get a cut).

Some types of MDS are mild and easily managed, while other types are severe and life-threatening. Mild MDS can grow more severe over time. It can also develop into a fast-growing, severe leukemia called acute myelogenous leukemia (AML).

About 19,000 people are diagnosed with MDS in the United States each year.1 Although MDS can affect people of any age, the majority are older than 60 years. Exposure to certain industrial chemicals or radiation can increase the risk of developing MDS. In some cases, MDS is caused by chemotherapy used to treat a different disease. This is called secondary MDS. In most cases, the cause of MDS is unknown.

There are many different types of MDS. Doctors look at cells in the blood and in the bone marrow to determine what type of MDS a patient has. Long-term survival and the risk that MDS might turn into AML are different for each type of MDS.

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1Howlader N, Noone AM, Krapcho M, Garshell J, Neyman N, Altekruse SF, Kosary CL, Yu M, Ruhl J, Tatalovich Z, Cho H, Mariotto A, Lewis DR, Chen HS, Feuer EJ, Cronin KA (eds). SEER Cancer Statistics Review, 1975-2010, National Cancer Institute. Bethesda, MD,, based on November 2012 SEER data submission, posted to the SEER web site, April 2013.