Descriptive epidemiology of childhood leukaemia.

Internationally there is a 4-fold variation in age-adjusted incidence rates for childhood leukaemia (all types combined), with only slightly greater worldwide differences specifically for acute lymphocytic leukaemia (ALL) and for acute nonlymphocytic leukaemia (ANLL). Total leukaemia rates are highest among Hispanic populations in Costa Rica and Los Angeles (males), due primarily to elevated ALL incidence, while low rates occur among US blacks, Kuwaitis, Israeli non-Jews, and Bombay Indians. In most populations the patterns for ALL are similar to those for total leukaema, with peak incidence at ages 1-4 and a decline thereafter. Lower and more uniform rates are generally observed at all ages for ANLL. Age-adjusted rates for ANLL appear to vary substantially among some populations with uniform ALL incidence rates (e.g., among Asians) and yet appear to be similar in other populations with variation in ALL rates (e.g., whites and blacks in the US). Possible variation among registries in completeness of childhood leukaemia ascertainment and accuracy of diagnosis by cell type should be assessed, while case-control investigations among populations with very high and very low rates may provide useful information about the cell-type specific determinants of childhood leukaemia.