The incidence of this disease in the UK has increased dramatically during the last century, mainly in the under-five age group, in whom the risk increased by more than 50 per cent in the second half of the century.

The reasons for this are not known but according to Alan Preece, Professor of Medical Physics at Bristol University, western England environmental factors are thought to play a major role in the increasing incidence. He explained that the unborn child is particularly sensitive to the effects of the mother’s exposure to environmental agents through placental transfer.

Preece and his team at Bristol set out to determine the extent of placental transfer through a series of bio-distribution measurements and ex-vivo experiments using donated human placentas. They found “reasonable correlation” between the placental transfer data from different models, allowing preliminary calculations of dose to foetal organs.

Professor Preece told delegates: “We found that foetal organ concentrations can exceed those of the mother which may have implications due to the increased sensitivity of the foetus. The exact levels are as yet unknown but we know that childhood leukaemia is initiated in utero and this could well be a factor in the initiation. Consideration must now be given to the likely risk estimates.”

Top international experts from Europe, the United States, Asia and Australia converged on London to discuss this and a wealth of other research presented over the five days of the conference. Many of the “usual suspects” were covered - including radiation, parental smoking, viruses and air pollution. But other concepts that have so far received little attention were also be highlighted. These include, for example, diet in early life, melatonin and circadian rhythms, light pollution and medicines in pregnancy.