Childhood cancer incidence: geographical and temporal variations.

Data from the first four volumes of Cancer Incidence in Five Continents (CI-5) and from the first 5 years of the US Surveillance, Epidemiology and End Results (SEER) program were analyzed for evidence of geographical and temporal variations in the incidence of selected childhood tumors. Only lymphoid leukemia and glial neoplasms are common enough for the observed differences between US registries to be distinguished from sampling variation. Internationally, kidney and eye tumors and leukemia show less geographical variation than do lymphomas and brain tumors, but for none of the tumors examined is the incidence constant. Wilms' tumor rates among Japanese, Singapore Chinese and Indians (Bombay) are approximately 60% of the rates in North America and Britain, whereas in Scandinavia the rates are up to 30% higher. This lessens the status of Wilms' tumor as an "index tumor" of childhood. Areas or countries with especially high or low rates of other tumors are identified. Rates for glial neoplasms (SEER data) and Hodgkin's disease (CI-5) are increasing with time in the US, while brain tumors are being diagnosed more frequently worldwide. However, the results for brain tumors may largely reflect changes in pathology diagnosis or reporting practices, and those for Hodgkin's disease may reflect improvements in case ascertainment. Otherwise, there is a remarkable stability in the incidence of selected childhood cancers over time.