Chronic eosinophilic leukemia (CEL) is a blood cancer that causes an excess of eosinophils in the body. Eosinophils are a type of white blood cell that help ward off infection, but having too many can be harmful.

CEL is rare, but researchers currently do not know its true incidence in the United States.

In this article, we look at the symptoms and causes of CEL, as well as the treatment options and outlook.

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CEL is a rare type of myeloproliferative neoplasm — a blood cancer that develops when stem cells in bone marrow, called myeloid stem cells, produce too many red and white blood cells and platelets.

CEL causes the body to overproduce a type of white blood cell called eosinophils. Eosinophils release chemicals to protect the body against certain infections or during an allergic reaction.

People with CEL have high levels of eosinophils in their bone marrow, blood, and other tissues. This can cause complications such as organ damage.

In the early stages of the disease, people may not have symptoms. And in some people without symptoms, a routine blood test indicates CEL.

Other people may have severe symptoms, due to the effects of high eosinophil levels.

Some symptoms of CEL may include:

  • fatigue
  • fever
  • cough
  • swelling under the skin around the eyes, lips, throat, hands, or feet
  • muscle aches or pains
  • itchiness
  • diarrhea
  • night sweats
  • unexplained weight loss
  • shortness of breath
  • swollen lymph nodes
  • anemia

People who receive a CEL diagnosis are usually around 20–50 years old, but it can also occur in children and older adults. CEL is more common in males than females.

There is no known cause of CEL. Researchers have found no link, for example, between CEL and a mutation in genes or chromosomes. In some rare cases, CEL may be due to environmental factors, such as smoking or exposure to radiation or certain chemicals.

In most cases, doctors aim to rule out all other possible causes of the person’s symptoms. If they then diagnose CEL, this is known as a diagnosis of exclusion.

A doctor assesses any symptoms, does a physical examination, and may then perform a range of tests, such as:

  • a complete blood count, which gives the amount and quality of white and red blood cells and platelets
  • blood chemistry tests, which show how well organs are functioning
  • a bone marrow biopsy and aspiration, which involves removing a small sample of bone marrow for testing

CEL is usually slow to progress and may remain the same for many years.

Sometimes, however, a person’s condition changes rapidly, as CEL turns into acute myelogenous leukemia.

A 2020 study involving participants in the U.S. who had CEL found a median survival time of 2 years after the diagnosis. In many of these participants, CEL developed into acute myelogenous leukemia.

Researchers behind a different 2020 study found that the outlook of CEL can vary, and they called for more research into this topic.

Other research found survival rates ranging from 8 months to 5 years in people who received stem cell transplantation as a treatment. Although this approach can be successful, doctors do not widely recognize it as a viable treatment for CEL.

The best approach may vary from person to person with CEL.

Corticosteroids, for example, and interferon alfa (Intron A, Wellferon) may help treat the disease. Doctors may also use chemotherapy drugs, such as:

  • hydroxyurea (Hydrea), possibly in combination with steroids
  • cyclophosphamide (Cytoxan, Procytox)
  • vincristine (Oncovin)

A doctor may recommend targeted chemotherapy drugs, which work on specific genes or parts of leukemia cells.

And treatment with the drug imatinib (Glivec) may lead to long-lasting remission in some people with CEL. This drug prevents the production of abnormal eosinophil levels.

If stem cells are available from a donor with similar genes, people with aggressive CEL may receive stem cell transplants.

To relieve symptoms of CEL, a doctor may recommend additional approaches, such as:

  • Leukapheresis: This involves an electrophoresis machine separating out excess white blood cells from the blood, reducing the number of eosinophils.
  • Blood-thinning medication: CEL can cause blood clots, and these drugs can help prevent the blood from clotting.
  • Splenectomy: High levels of eosinophils can cause the spleen to enlarge, leading to severe abdominal pain. In this case, a doctor may recommend surgery to remove the spleen.
  • Cardiac surgery: If people have heart disease, surgery to remove scarring of the heart muscle or replace heart valves may help improve the person’s heart function and prolong their life.

Hypereosinophilic syndrome (HES) refers to blood disorders that cause high levels of eosinophils. CEL is a type of HES.

An excess of eosinophils can affect various areas of the body, most commonly the:

In many cases, there is no known cause of HES. It can stem from increased production of a specific protein in certain white blood cells. In this case, a person has lymphocytic HES.

The disorder can also result from an inherited genetic mutation. In this case, a person has familial HES.

In someone with CEL, the high number of eosinophils results from changes to the bone marrow. CEL is a type of myeloproliferative HES.

Symptoms of HES may include:

  • skin rashes or swelling
  • breathing difficulties
  • stomach pain or upset
  • muscle and joint pain
  • problems with the nervous system, such as vertigo or tingling sensations
  • heart problems
  • anemia
  • deep vein thrombosis

Certain medications may help treat HES, including imatinib mesylate (Glivec) and mepolizumab (Nucala).

CEL is a rare type of blood cancer. It causes the body to overproduce a type of white blood cell called eosinophils.

Treatment may include medications, such as chemotherapy, and additional approaches, such as stem cell transplants or surgery.

CEL is slow to progress in many people, and treatment may result in long-term remission.