Leukemia is the most common type of cancer in children. The Leukemia and Lymphoma Society estimates that over 3,000 children will be diagnosed with leukemia in 2010. This condition starts in the bone marrow and affects production of blood cells. About half of all childhood leukemia cases occur by the age of 3.
Risk factors for leukemia include:
1. Gender. Males account for 57 percent of new cases.
2. Race. The incidence is highest in whites (12.9 per 100,000), and lowest in Native Americans (6.5 per 100,000).
3. Down syndrome.
4. Exposure to ionizing radiation. In some cases, radiation therapy for other cancers can produce leukemia.
However, all these risk factors together account for less than 10 percent of childhood leukemia cases. Researchers continue to look for risk factors that can be modified.
Most childhood leukemia cases are characterized by obvious abnormalities in the chromosomes, suggesting that genetic damage to the parents could be the cause. In animal models, chromosome damage to both males and females can produce blood cancers in their offspring. In humans, men have experienced DNA damage detectable in the sperm cells. The United States Environmental Protection Agency has identified 165 pesticide chemicals as known, probable, or possible human carcinogens. Based on these data, a Canadian research team reviewed the medical literature for associations between childhood leukemia and parental exposure to pesticides.
Occupational exposure to pesticides, mostly in farm workers, may represent the highest levels of risk from these chemiclas. The Canadian review article found 31 studies reported during the time period 1950 to 2009. The combined data show a significant association between pesticide exposure during pregnancy and childhood leukemia. For fathers exposed to pesticides before conception, there is not a significant association.
In a second paper, the researchers reviewed studies linking residential pesticide exposure to childhood leukemia. The quantities of pesticides used at home are expected to be much smaller than those used in agriculture.