What is childhood leukemia?
Leukemia is a type of cancer that starts in early forms of blood cells. Cancer starts when cells grow out of control. Cells in nearly any part of the body can become cancer. To learn more about how cancers start and spread, see What Is Cancer? For information about the differences between childhood cancers and adult cancers, see Cancer in Children.
Most of the time, leukemia is a cancer of the white blood cells, but some leukemias start in other kinds of blood cells. Leukemia starts in the bone marrow, the soft inner part of certain bones where new blood cells are made, and quickly spreads to the blood. From there it can go to other parts of the body.
Some other types of childhood cancer, such as Wilms tumor (a kidney cancer), can start in other organs and then spread to the bone marrow (or elsewhere). But those cancers are not leukemia.
Normal bone marrow and blood cells
To understand the different types of leukemia, it helps to know something about the bone marrow and blood.
Bone marrow is the soft, inner part of bones. It is where new blood cells are made. In babies, new blood cells are made in nearly all of the bones of the body. But by the teenage years they are made mostly in the flat bones (the skull, shoulder blades, ribs, hip bones, and back bones.
Bone marrow is made up of a small number of blood-forming cells (blood stem cells), other early forms of blood cells, fat cells, and tissues that help the blood cells grow. Early blood cells can grow to become red blood cells, white blood cells, or platelets.
Types of blood cells
Red blood cells carry oxygen from the lungs to all other tissues of the body and take carbon dioxide back to the lungs to be removed.
White blood cells help the body fight infections. There are many types of white blood cells, but the main types are:
Platelets are actually pieces that break off from certain bone marrow cells. Platelets help stop bleeding by plugging holes in blood vessels caused by cuts or bruises.
Types of leukemia in children
Leukemia can be either fast growing (acute), or slower growing (chronic). Almost all leukemia in children is acute.
There are 2 main types of acute leukemia:
- Acute lymphocytic leukemia (ALL), also called acute lymphoblastic leukemia, accounts for about 3 out of 4 childhood leukemias. ALL starts from early forms of lymphocytes in the bone marrow.
- Acute myelogenous leukemia (AML), also called acute myeloid leukemia, accounts for most of the remaining cases. This leukemia starts from the cells that form white blood cells (other than lymphocytes), red blood cells, or platelets.
- Hybrid or mixed lineage leukemias are rare. The cells have features of both ALL and AML. In children they are most often treated like ALL and usually respond to treatment like ALL.
Both ALL and AML have different subtypes as well.
Chronic leukemias are much more common in adults than in children. They are divided into 2 main types:
- Chronic myeloid leukemia (CML) is rare in children.
- Chronic lymphocytic leukemia (CLL) is almost never seen in children.
Juvenile myelomonocytic leukemia (JMML)
This rare type of leukemia is neither chronic nor acute. It’s not as fast growing as AML or as slow as CML. It occurs most often in children under age 4. Symptoms can include pale skin, fever, cough, easy bruising or bleeding, trouble breathing (from too many white blood cells in the lungs), and a swollen spleen and lymph nodes.
How common is childhood leukemia?
Leukemia is the most common cancer in children and teens. It accounts for almost 1 in 3 cancers in children. Even so, childhood leukemia is a rare disease.
About 3 out of 4 leukemias among children and teens are acute lymphocytic leukemia (ALL). Most of the rest are acute myelogenous leukemia (AML).
ALL is most common in early childhood, peaking in children between 2 and 4 years old. AML is more spread out across the childhood years, although it is slightly more common during the first 2 years of life and during the teen years.
Chronic leukemias are rare in children. Most of these are chronic myelogenous leukemia (CML), which tends to occur more in teens than in younger children.
Juvenile myelomonocytic leukemia (JMML) usually occurs in young children, with an average age of about 2.
Last Medical Review: 05/13/2015
Last Revised: 02/03/2016