There are several main types of leukemia in children.
Acute lymphocytic leukemia (ALL)
Acute lymphocytic leukemia (ALL), also called lymphoblastic or lymphoid, accounts for approximately 75% of childhood leukemia.
In this form of the disease, the lymphocyte cell line is affected. The lymphocytes normally fight infection. With acute lymphocytic leukemia, the bone marrow makes too many of these lymphocytes and they do not mature correctly. The lymphocytes overproduce and crowd out other blood cells. Immature blood cells (blasts) do not work properly to fight infection. Acute leukemia can occur over a short period of days to weeks. Chromosome abnormalities (extra chromosomes and structural changes in the chromosome material) are present in the majority of the blast cells of ALL patients.
Acute myelogenous leukemia (AML)
Acute myelogenous leukemia (AML), also called granulocytic, myelocytic, myeloblastic or myeloid, accounts for approximately 19% of childhood leukemia.
Acute myelogenous leukemia is a cancer of the blood in which too many granulocytes, a type of white blood cell, are produced in the marrow. The granulocytes normally fight infection. With acute myelogenous leukemia, the bone marrow makes too many of these cells and they do not mature correctly. The granulocytes overproduce and crowd out other blood cells. Immature blood cells (blasts) do not work properly to fight infection. Acute leukemia can occur over a short period of days to weeks. Children with certain genetic syndromes, including Fanconi anemia, Bloom syndrome, Kostmann syndrome and Down syndrome, are at a higher risk of developing AML than other children.
Chronic myelogenous leukemia (CML)
Chronic myelogenous leukemia (CML) is uncommon in children. Chronic myelogenous leukemia is cancer of the blood in which too many granulocytes, a type of white blood cell, are produced in the marrow. The granulocytes normally fight infection. With this disease, the bone marrow makes too many of these cells and they do not mature correctly. The marrow continues to produce these abnormal cells which crowd out other healthy blood cells.
Chronic myelogenous leukemia can occur over a period of months or years. A specific chromosome rearrangement is found in patients with CML. Part of chromosome #9 breaks off and attaches itself to chromosome #22, so that there is an exchange of genetic material between these two chromosomes. This rearrangement changes the position and functions of certain genes, which results in uncontrolled cell growth. Other chromosome abnormalities can also be present.