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Cancer starts when cells in the body start to grow out of control. Cells in nearly any part of the body can become cancer. To learn more about cancer and how it starts and spreads, see What Is Cancer? For information about the differences between childhood cancers and adult cancers, see Cancer in Children.
Leukemias are cancers that start in cells that would normally develop into different types of blood cells. Most often, leukemia starts in early forms of white blood cells, but some leukemias start in other blood cell types..
There are different types of leukemia, which are based mainly on:
Knowing the specific type of leukemia a child has can help doctors better predict each child’s prognosis (outlook) and select the best treatment.
Most childhood leukemias are acute. These leukemias can progress quickly, and typically need to be treated right away. The main types of acute leukemia are:
Rarely, acute leukemias can have features of both ALL and AML. These are called mixed lineage leukemias, acute undifferentiated leukemias, or mixed phenotype acute leukemias (MPALs). In children, they are generally treated like ALL and usually respond to treatment like ALL.
Both ALL and AML have subtypes. These are described in Childhood Leukemia Subtypes.
Chronic leukemias are rare in children. These leukemias tend to grow more slowly than acute leukemias, but they are also harder to cure. Chronic leukemias can be divided into 2 main types:
This rare type of leukemia is neither chronic nor acute. It starts in myeloid cells, but it usually doesn’t grow as fast as AML or as slowly as CML. It occurs most often in young children (average age of 2 years). Symptoms can include pale skin, fever, cough, easy bruising or bleeding, trouble breathing (from too many white blood cells in the lungs), rash, and an enlarged spleen, liver, and lymph nodes. For info on treating JMML, see Treatment of Children With Juvenile Myelomonocytic Leukemia (JMML).
To understand leukemia, it helps to know about the bone marrow, blood, and lymph systems.
Bone marrow is the soft inner part of certain bones. It is made up of blood-forming cells, fat cells, and supporting tissues. A small number of the blood-forming cells are blood stem cells.
Blood stem cells go through a series of changes to make new blood cells. During this process, the cells become either lymphocytes (a kind of white blood cell) or other blood-forming cells, which are types of myeloid cells. Myeloid cells can develop into red blood cells, white blood cells (other than lymphocytes), or platelets.
Red blood cells (RBCs) carry oxygen from the lungs to all other tissues in the body, and take carbon dioxide back to the lungs to be removed.
Platelets are actually cell fragments made by a type of bone marrow cell called the megakaryocyte. Platelets are important in stopping bleeding by plugging up holes in blood vessels.
White blood cells (WBCs) help the body fight infections. There are different types of white blood cells:
Leukemia starts in the bone marrow. The leukemia cells can build up there, crowding out normal cells. Most often, the leukemia cells spill into the bloodstream fairly quickly. Some types of leukemia can also spread to other parts of the body such as the lymph nodes, spleen, liver, central nervous system (the brain and spinal cord), testicles, or other organs.
Some other childhood cancers, such as neuroblastoma or rhabdomyosarcoma, start in other organs and can spread to bone marrow, but these cancers are not leukemia.
The American Cancer Society medical and editorial content team
Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.
Caywood EH, Kolb EA. Juvenile myelomonocytic leukemia. UpToDate. 2018. Accessed at www.uptodate.com/contents/juvenile-myelomonocytic-leukemia on November 29, 2018.
Rabin KR, Gramatges MM, Margolin JF, Poplack DG. Chapter 19: Acute Lymphoblastic Leukemia. In: Pizzo PA, Poplack DG, eds. Principles and Practice of Pediatric Oncology. 7th ed. Philadelphia Pa: Lippincott Williams & Wilkins; 2016.
Rabin KR, Margolin JF, Kamdar KY, Poplack DG. Chapter 100: Leukemias and Lymphomas of Childhood. In: DeVita VT, Lawrence TS, Rosenberg SA, eds. DeVita, Hellman, and Rosenberg’s Cancer: Principles and Practice of Oncology. 10th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2015.
Last Revised: February 12, 2019
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