Myeloid malignancies are cancers that affect one family of cells in the blood and bone marrow. Bone marrow is the soft, inner component of the bone. All types of blood cells are produced in the bone marrow, including:

• White blood cells – cells that fight infection
  
  
• Red blood cells – cells that carry oxygen to tissues all over the body
  
  
• Platelets – cells that help develop blood clots and control bleeding

There are three types of myeloid malignancies that can occur in children:

• Acute myeloid leukemia (AML). The most common type of childhood myeloid malignancy. In AML, the bone marrow manufactures a large number of abnormal blood cells. Over time these cells begin to build up, crowding out normal white blood cells, red blood cells and platelets. The result is a type of leukemia that quickly spreads from bone marrow into the bloodstream.
  
  
• Myelodysplastic syndromes (MDS). A group of conditions caused by changes in the blood-forming cells of the bone marrow. Although it is most common in adults over the age of 70, it can occur in children. In MDS, the stem cells do not mature into healthy red blood cells, white blood cells or platelets. In some children, myelodysplastic syndromes can progress to AML.
  
  
• Juvenile myelomonocytic leukemia (JMML). A type of myeloid malignancy in which the bone marrow produces too many white blood cells.  JMML is a rare form of childhood leukemia that produces many of the same symptoms as AML.

The exact cause of these diseases has not been identified. Researchers, however, have gained a greater understanding of how specific changes in DNA can cause bone marrow cells to develop into leukemia and myelodysplastic syndromes. A number of risk factors have been identified, including treatment for previous cancers and certain genetic syndromes. 

Symptoms of myeloid malignancies vary depending on where they have spread in the body. General signs and symptoms include weight loss, fever, loss of appetite and weakness.

Although symptoms and a physical examination may suggest a myeloid malignancy, additional tests, including bone marrow tests, are typically necessary to verify the diagnosis.

The treatment and prognosis for a myeloid malignancy depends on the subtype of the disease, as well as certain additional factors including the patient’s age. Typical treatment includes chemotherapy, radiation therapy, and bone marrow/stem cell transplantation. Individuals with myeloid malignancies may receive a combination of these therapies.