General Information and Causes
Leukemia, which is cancer of the bone marrow and blood, is the most common of childhood cancers, causing more deaths than any other form of cancer among those under 20 years of age2.
There are four major types of leukemia.
- Acute lymphocytic ( or lymphoblastic) leukemia (ALL)
- Acute myeloid leukemia (AML)
- Chronic Lymphocytic Leukemia (CLL)
- Chronic myeloid leukemia (CML)
In children, the majority of leukemias are rapidly progressing in nature (acute) rather than slow developing (chronic). ALL comprises about 75% of new leukemia diagnoses in children, and AML comprises the bulk of the remaining diagnoses. CML and other forms, such as hybrid leukemias or juvenile myelomonocytic leukemia (JMML), are much less common3.
ALL is most common in early childhood, especially between 2 and 4 years of age. AML is slightly more common during the first 2 years of life and during the adolescent years than during the intervening years of childhood3.
Race and sex also factor into the distribution of ALL, which is slightly more common among white children, and among boys. These factors do not influence the distribution of AML3.
The incidence of childhood cancer has increased slightly by 0.5% per year from 2004 to 2008, maintaining the upwards trend noted since 1975. In particular, incidence rates of childhood ALL and AML have increased between 1992 and 20064,5.
Experts estimate that pure genetic factors account for no more than 20% of all childhood cancers. They further estimate that depending on the type of cancer, anywhere between 5% - 90% may be attributable, in whole or in part, to environmental factors, including those likely arising from gene-environment interactions6. This means that a potentially large percentage of childhood cancers may be preventable.
There have been few environmental exposures considered to be "established" factors of childhood leukemia, including ionizing radiation and certain chemotherapeutic agents. However, there is mounting evidence that parental and childhood exposures to certain toxic chemcials may increase the risk of developing childhood leukemia. In addition to ionizing radiation and previous chemotherapy, the exposure associations with the strongest and most consistent evidence are pesticides7,8,9,10, tobacco smoke11,12,13,14, and paints and solvents15,16,17,18,19.
Click here for our Parent/Care-giver fact sheet on childhood leukemia and tips to reduce exposure to environmental risk factors.