The acute leukemias are the most common childhood cancers. This article provides a review of the epidemiology of childhood acute lymphoblastic leukemia (ALL) and non-acute lymphoblastic leukemia (ANLL), including descriptive characteristics in addition to environmental and genetic associations. The need for more focused studies of particular subgroups of ALL and ANLL is discussed.
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as opposed to race itself. This view is supported in part by the delayed occurrence of the 3-to 5-year-old incidence peak in American blacks. Seasonal variations in the incidence of childhood ALL have been the subject of several investigations. These studies have been motivated in part to assess possible associations between infectious outbreaks and the incidence of ALL, and the observed seasonal variations in incidence in some adult cancers. 24 As noted in a recent review of the epidemiology of childhood cancer, 55 while seasonal variations have been observed in some studies, others have failed to identify differences. Moreover, there has been an overall inconsistency in the seasons associated with an increased incidence as well as the number of seasonal peaks occurring in a year. This lack of consistency and the lack of an apparent biologic justification for a seasonal variation makes the importance of these findings unclear. A finding that has aroused much interest has been the geographic variations in the incidence of ALL that has been seen in the United States. A significantly higher ALL mortality was noted in the upper Midwestern states in the 1956 study of Walter and Gilliam. 134 The rates of ALL in these states were up to 28 per cent higher than in most others. Speculation regarding potential reasons for this increase focused on pesticide and herbicide exposure as a result of the agricultural nature of these states, as well as a potential zoonotic transmission of an infectious agent. Interest in potential environmental influences has also been generated by studies of the occurrence of ALL in migrant populations, in particular, studies of Arab populations along the Gaza strip in Israel. Ramot has observed an evolution of the patterns of malignancy in this population from predominantly B-cell lymphomas to T-cell ALL to common ALL. These studies have supported the possible role of environmental factors in determining the potential expression of malignancy, particularly in this population and potentially in others.loo Additional international data show a marked disparity in the incidence of childhood ALL worldwide with a lower disease incidence in Africa and the Mideast and higher rates in China, Japan, United States, England, and Europe. 55