Myelodysplastic syndromes, also called pre-leukemia or “smoldering” leukemia, are diseases in which the bone marrow does not function normally and not enough normal blood cells are made. The bone marrow is the spongy tissue inside the large bones in the body. The bone marrow makes red blood cells (which carry oxygen and other materials to all tissues of the body), white blood cells (which fight infection), and platelets (which make the blood clot). Normally, bone marrow cells called blasts develop (mature) into several different types of blood cells that have specific jobs in the body.

Myelodysplastic syndromes occur most often in older people, but they can occur in younger people. The most common sign is anemia, which means there are too few mature red blood cells to carry oxygen. There may also be too few white blood cells in the blood to fight infections. If the number of platelets in the blood is lower than normal, this may cause people to bleed or bruise more easily. A doctor should be seen if a person bleeds without any reason, bruises more easily than normal, has an infection that won’t go away, or feels tired all the time.

If there are symptoms, a doctor may order blood tests to count the number of each kind of blood cell. If the results of the blood test are not normal, the doctor may do a bone marrow biopsy. During this test, a needle is inserted into a bone and a small amount of bone marrow is taken out and looked at under the microscope. The doctor can then determine the kind of disease and plan the best treatment.

A myelodysplastic syndrome may develop following treatment with drugs or radiation therapy for other diseases, or it may develop without any known cause. The myelodysplastic syndromes may change into acute myeloid leukemia, a form of cancer in which too many white blood cells are made.

Myelodysplastic syndromes are grouped together based on how the bone marrow cells and blood cells look under a microscope. There are five types of myelodysplastic syndromes: refractory anemia, refractory anemia with ringed sideroblasts, refractory anemia with excess blasts, refractory anemia with excess blasts in transformation, and chronic myelomonocytic leukemia.