Discussion and summary

The presentations at this workshop demonstrate that, while there have been tremendous strides in the ability to cure childhood leukaemias, the understanding of the genetic and environmental causes of this class of diseases is limited. The epidemiological and the molecular evidence all suggest that childhood leukaemia derives from a multistage process where the initial event starting the process is either inherited or the result of a DNA damaging event during gestation(1). From that initial event, the progression to disease has to occur fairly rapidly because the peak incidence occurs very early in life at around 1–3 y of age depending upon the type of leukaemia(2,3). At later ages, the incidence drops off quite dramatically with a >90% smaller incidence beyond age 15. As discussed at the workshop and in the articles in this special edition, a large number of studies have been conducted to identify risk factors associated with and possibly causal of childhood leukaemia. It is clear from the reviews in this special edition that the only environmental factor that is clearly linked to childhood leukaemia and most likely causes a fraction of the cases is ionizing radiation(4). Extremely low-frequency electric and magnetic fields (EMFs) have also been associated with childhood leukaemia, but most reviews of this literature have found these studies to provide only limited evidence of an association, which is insufficient for a causal association(5). Other environmental factors such as radiofrequency EMF, air pollution, smoking, pesticides, herbicides, persistent organic pollutants, radon gas and solvents, have all yielded either very weak associations or no association at all(4). Indirect indicators of environmental exposures, such as proximity to nuclear power plants, have not provided any additional evidence of a causal exposure.