Methodologic approaches to studying environmental factors in childhood cancer.

Little is known about environmental causes of childhood cancer. This is probably due to the relative rarity of cancer in children. In the United States, cancer incidence in adults is over 20 times greater than cancer incidence in children. The situation is compounded by the fact that two groups of cancers, leukemias and brain and spinal tumors, account for half of all childhood cancers. The rarity of childhood cancer renders the conduct of most cohort studies infeasible. The majority of studies assessing potential environmental risk factors for childhood cancers have been case-control studies, which are highly efficient for studying rare diseases. Case-control studies of childhood cancers have been greatly facilitated by using cooperative clinical trial groups for case identification. The national studies that have emerged utilize random-digit telephone dialing and telephone interviewing as feasible and economic means of identifying and interviewing controls. Other approaches such as descriptive epidemiology, ecologic studies, and studies of cancer clusters have proven to be disappointing in elucidating environmental causes of childhood cancer. Descriptive and ecologic studies provide no information on specific exposures of study subjects; rather, they use population levels as surrogates for individual exposure. Studies of cancer clusters have also proven to be disappointing. Although there are numerous difficulties in conducting research on the causes of childhood cancer, these difficulties can be remedied by using carefully designed and conducted studies. It should be remembered that the epidemiologic approach is probably the most likely research venue for uncovering environmental causes of childhood cancer.