What Is Leukemia?
Learn more about cancers of the bone marrow and blood cells.

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Picture of woman reading information What Is Leukemia?

Leukemia is a type of cancer that affects the bone marrow, the soft center of large bones. Bone marrow produces blood cells. To understand leukemia, it helps to know more about normal blood cells.

There are 3 main types of blood cells:

  • White blood cells (leukocytes) help the body fight infections and other diseases.
  • Red blood cells (erythrocytes) carry oxygen from the lungs to the body's tissues.
  • Platelets help form blood clots that control bleeding.

Normally, bone marrow makes these cells in an orderly, controlled way, as the body needs them. They travel through the bloodstream doing their jobs. When they get old or damaged, they die, and new blood cells are made to take their place.

In leukemia, this process gets out of control. The marrow starts producing too many abnormal white blood cells called leukemia cells. Leukemia means "white blood." These cells don't work properly, and they don't die off as they should. As their numbers continue to grow, they crowd normal blood cells. This can lead to:

  • A weak immune system, which can result in recurrent infections or poor wound healing
  • Anemia, which can cause fatigue and weakness
  • Bruising and bleeding

A test called a complete blood count (CBC) can show that the blood cell types are out of balance. To diagnose the type of leukemia, a sample (or biopsy) of bone marrow is taken using a long, hollow needle. This is called a bone marrow aspiration or bone marrow biopsy.

The 4 most common types of leukemia are described according to how quickly the disease develops (acute or chronic) and by the type of white blood cell affected (myelogenous or lymphocytic). Acute leukemia progresses quickly and requires immediate treatment. Chronic leukemia progresses slowly. Treatment may not be needed until symptoms occur.

Facts about leukemia
Leukemia is the most common cancer in children younger than age 7. It accounts for nearly one third of cancer cases in children younger than 15.

  • Although it occurs in children, leukemia is almost 10 times more common in adults than in children.
  • Most cases of leukemia occur in older adults. The incidence of leukemia rises sharply after age 50. The median age at the time of diagnosis is 66 years.
  • The most common types of leukemia in adults are chronic lymphocytic leukemia (CLL) and acute myelogenous leukemia (AML). The most common type of leukemia in children is acute lymphocytic leukemia (ALL).
By Lila Havens, Staff Writer
Created on 11/26/1999
Updated on 05/25/2011
  • National Cancer Institute. What you need to know about leukemia.
  • Leukemia and Lymphoma Society. Leukemia.
  • Landgren O, Albitar M, Ma W, et al. B-cell clones as early markers for chronic lymphocytic leukemia. New England Journal of Medicine. 2009;360(7):659-667.
  • American Society of Clinical Oncology. Leukemia - chronic lymphocytic - CLL.
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