The relative frequencies of the common malignancies of childhood were abstracted from volmes I and II of Cancer Incidence in Five Continents. Those registries represented in both volumes were compared from one period to the next within and between registries. It was found that there was no significant variation of the relative frequencies within registries while the difference between registries was highly significant. These findings are best accounted for by attributing childhood neoplasms to heredity. The gene or genes predisposing to neoplasia are either ‘switched on’ spontaneously or by external oncogenic agents, the neoplasm which eventuates being a function of the genes. Environmental oncogenic agents influence the number of cancers appearing in a particular community but not their proportions relative to one another since cancer genotypes appear to be in Hardy-Weinberg equilibrium in any given population of children.
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