The primary goal of the Childhood Cancer Research Core is to identify environmental factors responsible for childhood cancer. Specific aims are to understand the interactions between environmental causes of childhood cancer and host factors that influence reaction to environmental exposure.

The etiology of childhood cancer has been a long-standing interest of faculty in the USC Department of Preventive Medicine. Epidemiological study of these cancers has been hampered by their rarity, but a number of factors have assisted us in the development of our Childhood Cancer Research Core. The first is the population base of the Los Angeles County Cancer Surveillance Program, a tumor registry which has provided an adequate number of cases for several case-control studies of the two commonest malignancies, acute leukemia and brain tumors. The second are the collaborative links established by Dr. Preston-Martin, both within the U.S. and internationally (through the IARC), to expand the population base for her research on the causes of childhood brain tumors. Third, Drs. Buckley, Bhatia and VanTornout have directed most of their research through the Children’s Cancer Group, a cooperative clinical cancer trials group that collectively treated over half the children with cancer in the United States. While we are far from understanding the basis of most childhood cancers, the picture that has emerged from recent research of this group, and others, is as follows. There are clearly heritable genetic factors responsible for some cancers (notably, retinoblastoma), but family studies in general suggest that the contribution of such factors is small. On the other hand, there is substantial evidence implicating a number of environmental factors in childhood cancer, including both direct exposures to the child and indirect parental exposures.

Controversy has arisen recently regarding the apparent increase in incidence of childhood cancer in the U.S. Some investigators, particularly at the EPA, have raised concerns that this increase may reflect new or increasing environmental exposures. The alternative view is that there has been little secular change in incidence, and that apparent increases in, for example, brain tumors, reflect changes in medical practice and diagnostic methods rather than a true increase in incidence. Part of the difficulty in understanding childhood cancer trends lies in the relative rarity of most cancer types and the lack of a national system of cancer registration that would provide the ability to track incidence on a nation-wide scale.

For the most part, environmental associations that have been reported for childhood cancers have been of moderate magnitude (and thus readily interpretable as due to unrecognized confounding) and relatively inconsistent across studies. The challenge for the future is to confirm the genuine associations through larger, more focused studies, and to reduce potential bias and increase the accuracy and specificity of the exposure assessments through direct measurement where possible.