Myelodysplastic Syndrome Overview

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What Is Myelodysplastic Syndrome? TOPICS

What are myelodysplastic syndromes?

Myelodysplastic syndromes (MDS) are conditions that occur when the blood-forming cells in the bone marrow are damaged. This damage leads to low numbers of one or more types of blood cells.

Normal bone marrow

Bone marrow is the soft, inner part of some bones, such as those of the skull, shoulder blades, ribs, pelvis, and backbones. Bone marrow contains stem cells that divide to form new cells. When a stem cell divides it makes 2 cells: one cell that stays a stem cell, and another cell that can make other kinds of blood cells. There are 3 kinds of blood cells: red blood cells, white blood cells, and platelets.

  • Red blood cells carry oxygen from the lungs to the rest of the body and carry away carbon dioxide.
  • White blood cells help the body fight infection. There are many types of white blood cells.
  • Platelets are pieces of cells. They are needed for the blood to clot. They help plug up damaged areas of blood vessels caused by cuts or bruises.

Myelodysplastic syndromes

In MDS, some of the cells in the bone marrow are damaged and have problems making new blood cells. Many of the blood cells that are made by these damaged cells are not normal. The abnormal blood cells die sooner than normal cells, leaving the person without enough normal blood cells and with low blood counts.

MDS can turn into a fast-growing cancer of bone marrow cells called acute myeloid leukemia. This happens in about 1 out of 3 people with MDS. In the past, MDS was called pre-leukemia or smoldering leukemia. Since most MDS patients do not get leukemia, these terms are no longer used. Now that doctors have learned more about MDS, it is thought to be a form of cancer.

The American Cancer Society document, Leukemia: Acute Myeloid (Myelogenous) has more information about the leukemia that develops in some MDS patients.

Types of MDS

The system used to classify MDS is known as the WHO (World Health Organization) system. This system divides MDS into 7 groups. The group depends on how the cells of the blood and bone marrow look under a microscope and the presence of certain changes in the chromosomes of those cells. Because the differences can be very small, doctors might not agree about which group a patient’s disease belongs in. Your doctor can explain to you the exact kind of MDS you have.

Cases of MDS can also be grouped based on the cause of the disease. (This is called clinical classification.) If no cause can be found, it is called primary MDS. It is called secondary MDS when the cause of the disease is known. Secondary MDS is often called treatment-related, because the most common cause is earlier treatment for cancer. Secondary MDS is much less likely to respond to treatment.


Last Medical Review: 02/27/2014
Last Revised: 04/03/2014