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Myelodysplastic syndromes (MDS), also known as myelodysplastic neoplasms, are conditions that can occur when the blood-forming cells in the bone marrow become abnormal, resulting in the marrow not making enough healthy new blood cells. This leads to low levels of one or more types of blood cells. MDS is considered a type of cancer.

How does MDS affect blood and bone marrow?

Bone marrow is the spongy substance inside the bone. It is made up of blood-forming cells, fat cells, and supporting tissues. A small fraction of the blood-forming cells are blood stem cells. These stem cells are needed to make new blood cells.

In myelodysplastic syndromes, some of the blood stem cells in the bone marrow are abnormal (dysplastic). They have problems making new blood cells. Many of the blood cells formed by these bone marrow cells are defective.

As these defective cells build up in the bone marrow, they can crowd out normal blood cells. When a person doesn’t have enough normal blood cells, they may have:

• Anemia (low red blood cells): Red blood cells (RBCs) carry oxygen throughout the body. Having too few RBCs can cause fatigue, weakness, shortness of breath, and pale skin (which may be harder to notice in people with darker skin).
• Neutropenia (low white blood cells): White blood cells (WBC) help fight infections. Having too few WBC can increase the risk of infections.
• Thrombocytopenia (low platelets): Platelets are small cell fragments that help the blood clot and stop bleeding.  Too few platelets can lead to abnormal bleeding or bruising.

Even if a person with MDS has a normal number of blood cells, those cells might be abnormal and may not function well. For example, abnormal white blood cells might not be able to fight infections well and abnormal platelets might not form clots as they should.

Is MDS a cancer or a pre-cancer?

In the past, MDS was sometimes referred to as pre-leukemia or smoldering leukemia. Now MDS is considered a form of cancer.

MDS can also develop into a more serious cancer. In about 1 in 3 people with MDS, the disease can progress to acute myeloid leukemia (AML), a fast-growing cancer of bone marrow cells.