National Cancer Institute Research on Childhood Cancers
In the United States in 2005, approximately 9,510 children under age 15 will be diagnosed with cancer and about 1,585 children will die from the disease. Although this makes cancer the leading cause of death by disease among U.S. children 1 to 14 years of age, cancer is still relatively rare in this age group with, on average, 1 to 2 children developing the disease each year for every 10,000 children in the United States.
Among the 12 major types of childhood cancers, leukemias and brain and other central nervous system tumors account for over one-half of the new cases. About one-third of childhood cancers are leukemias. The most common type of leukemia in children is acute lymphoblastic leukemia. The most common solid tumors are brain tumors, with other solid tumors being less common.
Over the past 20 years, there has been some increase in the incidence of children diagnosed with all forms of invasive cancer, from 11.5 cases per 100,000 children in 1975 to 14.6 per 100,000 children in 2002. During this same time, however, death rates declined dramatically and 5-year survival rates increased for most childhood cancers. For example, the 5-year survival rates for all childhood cancers combined increased from 55.9 percent in 1974–1976 to 78.6 percent in 1995–2001. This improvement in survival rates is due to significant advances in treatment, resulting in cure or long-term remission for a substantial proportion of children with cancer.
Long-term trends in incidence for leukemias and brain tumors, the most common childhood cancers, show patterns that are somewhat different from the others. Childhood leukemias appeared to increase in incidence in the early 1980s, with rates in the preceding years at fewer than 4 cases per 100,000. Rates in the succeeding years have shown no consistent upward or downward trend and have ranged from 3.7 to 4.8 cases per 100,000.
For childhood brain tumors, the overall incidence rose from 1975 through 2002, with the greatest increase occurring from l983 through l986. An article in the September 2, 1998, issue of the Journal of the National Cancer Institute suggests that the rise in incidence from 1983 through 1986 may not have represented a true increase in the number of cases, but may have reflected new forms of imaging equipment that enabled visualization of brain tumors that could not be easily visualized with older equipment. Other important developments during the 1983–1986 period included the changing classification of brain tumors, which resulted in tumors previously designated as “benign” being reclassified as “malignant,” and improvements in neurosurgical techniques for biopsying brain tumors.
The causes of childhood cancers are largely unknown. A few conditions, such as Down syndrome, other specific chromosomal and genetic abnormalities, and ionizing radiation exposures, explain a small percentage of cases.
Environmental causes of childhood cancer have long been suspected by many scientists but have been difficult to pin down, partly because cancer in children is rare, and partly because it is so difficult to identify past exposure levels in children, particularly during potentially important periods such as pregnancy or even prior to conception. In addition, each of the distinctive types of childhood cancers develops differently—with a potentially wide variety of causes and a unique clinical course in terms of age, race, gender, and many other factors.
A monograph based on data from the National Cancer Institute’s Surveillance, Epidemiology, and End Results Program was published in 1999 on U.S. trends in incidence, mortality, and survival rates of childhood cancers. In the monograph, information about known, suspected, and possible risk factors is summarized in more detail. It is available at http://seer.cancer.gov/publications/childhood/ on the Internet. More up-to-date incidence, mortality, and survival information for children is available at http://seer.cancer.gov/csr/1975_2002/sections.html on the Internet, in sections 28 and 29.