The incidence of childhood leukaemia increased dramatically in the twentieth century. The increase has mainly affected the under five age group, in whom the risk increased by more than 50 per cent during the second half of the century alone.

Although the causes of leukaemia in children are poorly understood, environmental factors are thought to play a major role in the rising incidence since changes in our genetic make up simply do not happen on this kind of timescale. If this is the case, then it may be possible to take preventative measures, but first we need to determine what these factors are. This is the driving force behind the conference - Childhood leukaemia: incidence, causal mechanisms and prevention - which is being hosted by CHILDREN with LEUKAEMIA, Britain's leading charity devoted to the conquest of the disease.

Whilst the link between leukaemia and light at night may, on the surface, seem surprising, it has a logical basis and there is considerable evidence pointing towards the association. Compared with 100 years ago we are exposed to considerable light at night (LAN) during the natural hours of darkness. LAN disrupts our natural circadian rhythm, suppressing the normal nocturnal production of the hormone melatonin. As Russel Reiter, Professor of Cellular and Structural Biology at the University of Texas, explains, a reduction in melatonin has been linked to cancer initiation as well as cancer progression. "As an anti oxidant, in many studies melatonin has been shown to protect DNA from oxidative damage. Once damaged, DNA may mutate and carcinogenesis may occur."

A number of studies have shown that people in occupations that expose them to LAN (i.e. night workers) experience a higher risk of breast cancer and that blind people, who are not vulnerable to reduced melatonin levels through LAN, have a lower incidence of cancer.

Russell Foster, Professor of Visual Neuroscience at Imperial College, London, will be exploring the mechanisms by which light regulates the circadian system. He explains "Embedded within the genes of us, and almost all life on earth, are the instructions for a biological clock that marks the passage of approximately 24 hours. Until we turned our nights into days, and began to travel in aircraft across multiple time zones, we were largely unaware of these internal clocks. These clocks drive or alter our sleep patterns, alertness, mood, physical strength, blood pressure and every other aspect of our physiology and behaviour." Professor Foster has detected novel photoreceptors in the eye and he will be sharing the clues about light perception pathways that his work is revealing.

Professor Reiter will introduce the link between magnetic fields and childhood leukaemia, an association which is now thought to be related to the light at night effect since magnetic fields also appear to reduce melatonin levels. Reiter will be reviewing a number of theoretical explanations for this effect. As he says "If, in fact, melatonin levels are altered by magnetic fields, a potential relationship between these fields and cancer, including leukaemia, would be possible."

Top international experts from Europe, America, Asia and Australia will converge on London to discuss this and a wealth of other research being presented over the five days of the conference. Many of the usual suspects will be covered - including radiation, viruses, parental smoking and air pollution. But other concepts that have so far received little attention will also be highlighted. These include, for example, diet in early life, medicines in pregnancy as well as the links with melatonin and light at night, outlined above.

It is hoped that out of the conference will be born an agenda for future research and CHILDREN with LEUKAEMIA will be launching a £1m fund to support research in priority areas.