What is childhood leukemia?
Leukemia is a cancer of the blood-forming cells. Most of time, it 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 parts of certain bones where new blood cells are made, and quickly spreads to the blood. From there it can go to the lymph nodes, spleen, liver, brain and spinal cord, and other organs.
In contrast, 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, blood, and lymphoid tissue
To understand the different types of leukemia, it helps to know something about the blood and lymph systems.
Bone marrow is the soft, spongy, inner part of bones. It is where all 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 such as those of the skull, shoulder blades, ribs, pelvis, 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.
Red 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.
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.
White blood cells
White blood cells (also called leukocytes) help defend the body against germs. There are quite a few types (and subtypes) of white blood cells. Each has a special role to play in protecting the body against infection. The 3 main types of white blood cells are lymphocytes, granulocytes, and monocytes.
- Lymphocytes: Lymphocytes are the main cells that make up lymphoid tissue, a major part of the immune system. The immune system helps the body fight off infections. More information about the lymphocytes is given below.
- Granulocytes: The main job of these white blood cells is to destroy germs. Granulocytes go through several changes as they grow from early cells to mature, infection-fighting cells.
- Monocytes: Monocytes are also important in protecting the body against germs. After a short time in the bloodstream, they enter tissues to become macrophages, which can destroy some germs by surrounding and "eating" them.
Lymphoid tissue is the main part of the immune system. It is found in many places throughout the body including lymph nodes, the thymus, the spleen, the tonsils and adenoids, and the bone marrow. It is also scattered within other systems such as the digestive system.
The main cell type that forms lymphoid tissue is the lymphocyte. These are the cells from which the most common type of leukemia in children, acute lymphocytic leukemia (ALL), develops. The 2 main types of lymphocytes are:
- B lymphocytes (or B cells)
- T lymphocytes (or T cells)
Normal T cells and B cells do different jobs within the immune system. Although both can develop into leukemia, B-cell leukemias are much more common than T-cell leukemias.
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 cases of childhood leukemia. This leukemia starts from the lymphoid cells 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 respond to treatment like ALL.
Chronic leukemia is also divided into 2 types. Chronic myeloid leukemia (CML) is rare in children. Chronic lymphocytic leukemia (CLL) is almost never seen in children and is not covered here.
Juvenile myelomonocytic leukemia (JMML)
This rare type of leukemia is neither chronic nor acute. It isn't as fast growing as AML or as slow as CML. It occurs most often in young children (under age 4). Symptoms can include pale skin, fever, cough, trouble breathing (due to too many white blood cells in the lungs), and a swollen spleen and lymph nodes.
Last Medical Review: 06/29/2012
Last Revised: 01/21/2013