Myelodysplastic syndromes (MDS) are a group of cancers in which immature blood cells in the bone marrow do not mature and therefore do not become healthy blood cells. Early on, there are typically no symptoms. Later symptoms may include feeling tired, shortness of breath, easy bleeding, or frequent infections. Some types may develop into acute myeloid leukemia.Risk factors include previous chemotherapy or radiation therapy, exposure to certain chemicals such as tobacco smoke, pesticides, and benzene, and exposure to heavy metals such as mercury or lead. Problems with blood cell formation result in some combination of low red blood cells, low platelets, and low white blood cells. Some types have an increase in immature blood cells, called blasts, in the bone marrow or blood. The types of MDS are based on specific changes in the blood cells and bone marrow.Treatments may include supportive care, drug therapy, and stem cell transplantation. Supportive care may include blood transfusions, medications to increase the making of red blood cells, and antibiotics. Drug therapy may include the medication lenalidomide, antithymocyte globulin, and azacitidine. Certain people can be cured with chemotherapy followed by a stem-cell transplant from a donor.About seven per 100,000 people are affected with about four per 100,000 people newly acquiring the condition each year. The typical age of onset is 70 years. The outlook depends on the type of cells affected, the number of blasts in the bone marrow or blood, and the changes present in the chromosomes of the affected cells. The typical survival time following diagnosis is 2.5 years. The conditions were first recognized in the early 1900s. The current name came into use in 1976.