Leukemia is a cancer that starts in early blood-forming cells found in the bone marrow, the soft inner part of certain bones. Most often, leukemia is a cancer of the white blood cells, but some leukemia start in other blood cell types. Any of the blood-forming cells from the bone marrow can turn into a leukemia cell. Once this change takes place, the leukemia cells no longer mature in a normal way.
Leukemia cells might reproduce quickly, and not die when they should. These cells build up in the bone marrow, crowding out normal cells. In most cases, the leukemia cells spill into the bloodstream fairly quickly. From there they can go 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, where they can keep other cells in the body from doing their jobs.
Leukemia is often described as being either acute (fast growing) or chronic (slow growing). Almost all childhood leukemia is acute.
Acute lymphocytic (lymphoblastic) leukemia (ALL): About 3 out of 4 childhood leukemias are ALL. This leukemia starts from early forms of lymphocytes in the bone marrow.
Acute myelogenous leukemia (AML): This type of leukemia, also called acute myeloid leukemia, acute myelocytic leukemia, or acute non-lymphocytic leukemia, accounts for most of the remaining cases. AML starts from the myeloid cells that form white blood cells (other than lymphocytes), red blood cells, or platelets.
Hybrid or mixed lineage leukemia: In these rare leukemias, the cells have features of both ALL and AML. In children, they are generally treated like ALL and usually respond to treatment like ALL.
Chronic leukemias are much more common in adults than in children. They tend to grow more slowly than acute leukemias, but they are also harder to cure. Chronic leukemias can be divided into 2 types.
Chronic myelogenous leukemia (CML): This leukemia rarely occurs in children. Treatment is similar to that used for adults (see “Treatment of children with chronic myelogenous leukemia”). For more detailed information on CML, see Leukemia–Chronic Myeloid.
Chronic lymphocytic leukemia (CLL): This leukemia is extremely rare in children. For more information on CLL, see Leukemia–Chronic Lymphocytic.
Juvenile myelomonocytic leukemia (JMML).
This rare type of leukemia is neither chronic nor acute. It begins from myeloid cells, but it usually doesn’t grow as fast as AML or as slow as CML.
It occurs most often in young 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 an enlarged spleen and lymph nodes.