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Childhood Cancer
Cancer in childhood is quite rare compared with cancer in adults, but it still causes the most deaths, other than injuries and accidents, among children 0-19 years of age.47
Childhood cancer is not a single disease, as it includes a variety of malignancies. The forms of childhood cancer that are most common vary at different ages.
Cancer Incidence and Mortality
The incidence of childhood cancer increased from 1975 until about 1990. The frequency of the disease appears to have become fairly stable overall since 1990. Mortality has declined substantially during the last 25 years, due largely to improvements in treatment.
The causes of cancer in children are poorly understood, though in general it is thought that different forms of cancer have different causes. Established risk factors for the development of childhood cancer include family history, genetic defects, radiation, and certain pharmaceutical agents used in chemotherapy.47 Evidence from epidemiological studies suggests that environmental contaminants such as pesticides and certain chemicals, in addition to radiation, may contribute to an increased frequency of some childhood cancers.32 Some studies have found that children born to parents who work with or use such chemicals are more likely to have cancer in childhood.48 It may be that the chemicals cause mutations in parents' germ cells that may increase the risk of their children developing certain cancers, or perhaps the parental exposure is passed on to the child while in utero, affecting the child directly. Children's direct exposures to such chemicals also may contribute to cancer.
- Age-adjusted annual incidence of cancer in children increased from 130 to 150 cases per million children between 1975 and 1995. The incidence appears to have leveled off after 1990. Mortality decreased from 50 to 30 deaths per million children during the same period.
- Rates of cancer incidence vary by age. Rates are highest among infants, decline until age 9, and then rise again with increasing age. Between 1986 and 1995, children under 5 and those aged 15-19 experienced the highest incidence rates of cancer at approximately 200 cases per million. Children aged 5-9 and 10-14 had lower incidence rates at approximately 110 and 120 cases per million respectively.
- Between 1992 and 1996, incidence rates of cancer were highest among whites at 160 per million. Hispanics were next highest at 150 per million. Asians and Pacific Islanders had an incidence rate of 140 per million, Black children had a rate of 120 per million, and Native Americans and Alaska Natives had the lowest at 80 per million. Data on the incidence of childhood cancer by race and ethnicity are shown in the data tables in Appendix A.
Childhood Cancer by Type
Trends in the total incidence of childhood cancer are useful indicators for assessing the overall burden of cancer among children. However, broad trends mask changes in frequency of individual cancers. Individual cancers often have patterns that diverge from the overall trend. Moreover, environmental factors may be more likely to contribute to some childhood cancers than to others.
Ionizing radiation, such as from x-rays, is a known cause of leukemia and brain tumors.49-50 There is suggestive-but not conclusive-evidence that parental exposures to certain chemicals may be a cause of leukemia, brain cancer, non-Hodgkin's lymphoma, and Wilms' tumor in children.51
A number of studies have evaluated the relationship between pesticide exposure and certain types of childhood cancer, and while the evidence is suggestive of a link, it is still not conclusive.47 Most studies of the relationship between pesticide exposure and leukemia and brain cancer show increased risks for children whose parents used pesticides at home or work, and for children who may be exposed to pesticides in the home.52-53 Evidence is limited but suggestive that non-Hodgkin's lymphoma in children may be linked to parental pesticide exposure and exposure to pesticides in the home.52 There is some evidence linking pesticide use to Wilms' tumor and Ewing's sarcoma.52
- Leukemia was the most common cancer diagnosis for children from 1973-1996, representing 25 percent of the total cancer cases. Incidence of acute lymphoblastic leukemia has increased moderately from 23 cases per million between 1973-1978 to approximately 27 cases per million between 1991-1996. Rates of acute myeloid leukemia have remained stable.
- Central nervous system tumors represented 17 percent of childhood cancers. The incidence of central nervous system tumors increased from approximately 23 per million in 1973-1978 to 29 per million in 1991-1996.
- Lymphomas, which include Hodgkin's disease and non-Hodgkin's lymphoma, represent approximately 16 percent of childhood cancers. Hodgkin's disease declined slightly from roughly 14 per million in 1973-1978 to approximately 13 per million in 1991-1996. Non-Hodgkin's lymphomas increased from 8.9 per million in 1973-1978 to approximately 11 per million in 1991-1996.
- Different types of cancer affect children at different ages. Neuroblastomas, Wilms' tumor (tumors of the kidney), and retinoblastoma (tumors in the eye) usually are found only in very young children. Leukemias and nervous system cancers are most common through age 14; lymphomas, carcinomas, and germ cell and other gonadal tumors are more common in those 15-19 years old.47