Childhood Cancer: Leukemia

The term leukemia refers to cancers of the white blood cells, which are also referred to as leukocytes or WBCs. When a child has leukemia, large numbers of abnormal white blood cells are produced in the bone marrow. These abnormal white cells crowd the bone marrow and flood the bloodstream, but they cannot perform their proper role of protecting the body against disease because they are defective.

As leukemia progresses, the cancer interferes with the body's production of other types of blood cells, including red blood cells and platelets. This results in anemia (low numbers of red cells) and bleeding problems, in addition to the increased risk of infection caused by white cell abnormalities.

As a group, leukemias account for about 25% of all childhood cancers and affect about 2,200 American young people each year. Luckily, the chances for a cure are very good with leukemia. With treatment, most children with leukemia are free of the disease without it coming back.

Types of Childhood Leukemia
In general, leukemias are classified into acute (rapidly developing) and chronic (slowly developing) forms. In children, about 98% of leukemias are acute.

Acute childhood leukemias are also divided into acute lymphocytic leukemia (ALL) and acute myelogenous leukemia (AML), depending on whether specific white blood cells called lymphyocytes, which are linked to immune defenses, are involved.

Approximately 60% of children with leukemia have ALL, and about 38% have AML. Although slow-growing chronic myelogenous leukemia (CML) may also be seen in children, it is very rare, accounting for fewer than 50 cases of childhood leukemia each year in the United States.

Risk for Childhood Leukemia

The ALL form of the disease most commonly occurs in younger children ages 2 to 8, with a peak incidence at age 4. But it can affect all age groups.

Children have a 20% to 25% chance of developing ALL or AML if they have an identical twin who was diagnosed with the illness before age 6. In general, nonidentical twins and other siblings of children with leukemia have two to four times the average risk of developing this illness.

Children who have inherited certain genetic problems - such as Li-Fraumeni syndrome, Down syndrome, Kleinfelter syndrome, neurofibromatosis, ataxia telangectasia, or Fanconi's anemia - have a higher risk of developing leukemia, as do children who are receiving medical drugs to suppress their immune systems after organ transplants.

Children who have received prior radiation or chemotherapy for other types of cancer also have a higher risk for leukemia, usually within the first 8 years after treatment.

In most cases, neither parents nor children have control over the factors that trigger leukemia, although current studies are investigating the possibility that some environmental factors may predispose a child to develop the disease. Most leukemias arise from noninherited mutations (changes) in the genes of growing blood cells. Because these errors occur randomly and unpredictably, there is currently no effective way to prevent most types of leukemia.