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Approved by the Cancer.Net Editorial Board, 05/2023

About the blood and bone marrow

Bone marrow is the spongy, red tissue found in the center of large bones. It stores immature cells called stem cells. Stem cells usually mature into white blood cells, red blood cells, and platelets during a process called hematopoiesis. These cells have different functions in the body:

  • Red blood cells carry oxygen throughout the body
  • White blood cells fight infection
  • Platelets form clots to stop bleeding

About myelodysplastic syndromes

Myelodysplastic neoplasms or syndromes, also known as MDS, are a group of blood and bone marrow disorders. MDS is considered a type of cancer.

In MDS, stem cells do not mature as expected. This means there are too many immature cells, called blasts, and abnormally developed cells, called dysplastic cells. There are also too few healthy mature cells, causing the bone marrow to not work well or to stop working. This means there are less healthy red blood cells, white blood cells, and/or platelets. The numbers of blood cells are often called blood cell counts (see Diagnosis).

People with MDS often have co-existing conditions caused by the decrease in healthy cells, including:

Dysplastic white blood cells and platelets, in particular, may not work well. Even if the number of blood cells is normal in a person with MDS, their blood and bone marrow cells can still be abnormal.

There are several subtypes of MDS. Some subtypes of MDS may eventually turn into acute myeloid leukemia (AML). AML is a cancer of the blood in which immature cells called blasts increase and grow more quickly.