Over 80 percent of solid tumors in adults develop in the glands or lining tissues of the breast, lung, intestinal or urinary tract and are called carcinomas. But over 90 percent of solid tumors of children are malignancies of muscle, bone, supporting tissues or blood vessels and are called sarcomas. The types of cancer seen in children, therefore, differ from those in adults not only in name but in their microscopic appearance.
What Causes It We do not know why children develop cancer. Occasionally there are clues from the environment or from a genetic inheritance pattern that a child may be at risk. But specific causes have not been identified. However, children with certain diseases do have an increased incidence of cancer
( See "Risk Factors" ).
For more than 30 years there have been reports of "clusters" or concentrations of childhood cancer developing in certain geographic areas. There were clusters of children with leukemia in Niles, Illinois, in 1963, in Woburn, Massachusetts, in 1979, and in central California in the early 1990s. But physicians have not been able to figure out the significance of these clusters.
It is believed that children are more likely than adults to develop leukemia as a result of exposure to radiation. Children exposed to the radiation of the atomic bomb blasts in Japan had an increased risk of acute leukemia in childhood, with the peak occurring about five years after exposure. A higher incidence of leukemia in children exposed to radiation after the accident in Chernobyl, USSR, is expected. Radiation treatment is useful in the treatment of many cancers in children, but there is risk that children cured of their first cancer may develop a second one partly related to the use of radiation therapy .
