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Approved by the Cancer.Net Editorial Board, 08/2017

Leukemia is a cancer of the blood cells. Leukemia begins when healthy blood cells change and grow out of control.

About blood cells

Blood cells are made in the bone marrow, the spongy tissue inside the larger bones in the body. Changes in the bone marrow cells can cause too many or too few of certain blood cells.

There are different types of blood cells:

  • Red blood cells that carry oxygen throughout the body
  • White cells that fight infection
  • Platelets that help the blood to clot

About leukemia

Types of leukemia are named after the specific blood cell that becomes cancerous, such as lymphoid or myeloid cells. Lymphoid cells are a type of white blood cell. Myeloid cells are bone marrow cells that turn into the cells that fight bacterial infections.

There are 4 main types of leukemia in adults:

About eosinophilia and eosinophilic leukemia

  • Eosinophilia is a condition that develops when the bone marrow makes too many eosinophils, a type of white blood cell. People can have many eosinophils without having leukemia. For example, sometimes the body makes too many eosinophils because of an allergy or an infection with a parasite. This type of eosinophilia is called secondary, or reactive, eosinophilia and is much more common than eosinophilic leukemia.Chronic eosinophilic leukemia is a subtype of clonal eosinophilia, meaning it is caused by a new genetic mutation or change in the blood cells. It is sometimes called hypereosinophilic syndrome (HES). This disease is classified as a myeloproliferative neoplasm (MPN). Myelo- means bone marrow and proliferative means too much blood cell growth.

    This section focuses on chronic eosinophilic leukemia. Acute eosinophilic leukemia is very rare and is treated similarly to acute myeloid leukemia (AML)