Found: the cause of leukaemia

CHILDHOOD LEUKAEMIA is caused by an infection and not by radiation or environmental pollution, according to one of the world's most eminent cancer specialists.

Sir Richard Doll, who first established the link between smoking and lung cancer, has given his full support to a controversial theory that cancer clusters, including those near to nuclear installations, are the result of a virus or other infectious agents. In a forthcoming article for the British Journal of Cancer, Sir Richard says that new research into the reasons why some children develop the blood cancer has now established the cause as an infection by an as-yet unidentified agent.

"What I'm saying, in layman's terms, is that we believe that the principal cause of childhood leukaemia is an infection of some sort. We can't say what it is but we now know where we've got to look," Sir Richard said yesterday.

For two decades scientists have been trying to explain why leukaemia in children - an exceptionally rare disease - clusters around certain industrial sites, in particular the Sellafield nuclear reprocessing plant in Cumbria. Several investigations by leading cancer experts, epidemiologists and radiobiologists, have failed to establish a link with radiation or any other single factor, such as chemical pollution.

However, a theory developed by Professor Leo Kinlen, a cancer epidemiologist at Oxford University, has gradually become the most convincing explanation of the clusters.

Professor Kinlen, who is funded by the Cancer Research Campaign and has no financial ties with the nuclear industry, believes childhood leukaemia is caused by viruses or other infectious agents being introduced into a local community by the mass movement of migrant workers. Some children may be more susceptible to developing leukaemia as a result of being exposed to an infectious agent that may have little or no effect on other children, Professor Kinlen suggested.

Heather Dickinson and Louise Parker of the Children's Cancer Research Unit at the University of Newcastle have produced a computer model of the Kinlen hypothesis and found that it can correctly predict the incidence of leukaemia according to the amount of population mixing involved.

Sir Richard believes this is the final piece of the jigsaw which validates Professor Kinlen's hypothesis as the most likely explanation for childhood leukaemia clusters around Sellafield and elsewhere. "My view now is that Kinlen's hypothesis should be considered as established. It indicates an infective cause," he said. Hecriticised the government's Committee on the Medical Aspects of Radiation in the Environment for downgrading the Kinlen hypothesis when it published its fourth report in 1996.

Sir Richard, who is now retired but takes an active interest in cancer epidemiology from his base at Oxford's Radcliffe Infirmary, said scientists can now concentrate on trying to find the infective agent responsible. "It is possibly a common virus which only in special circumstances actually gives rise to leukaemia, rather than some rare one - but that's speculation. All I can say is that we're now convinced that it must be infection," he said.

Professor Kinlen said he could not comment on the findings until they are published in the British Journal of Cancer.