COMPELLING evidence, published in today’s British Journal of Cancer, confirms that population mixing is likely to be responsible for the cluster of childhood leukaemia cases at Seascale near Sellafield.

The paper*, by researchers at Newcastle University, adds crucial weight to Prof Leo Kinlen’s theory that in rare cases exposure to a common unidentified infection through population mixing results in the disease.

This exposure is greater, Prof Kinlen funded by The Cancer Research Campaign says, when people from urban areas mix with rural communities eg when construction workers and nuclear staff move into the Sellafield area.

And, in an accompanying editorial, internationally renowned cancer expert, Sir Richard Doll, says: “The time has now come when Kinlen’s hypothesis of population mixing as a cause of childhood lymphoblastic leukaemia can be regarded as established.”

The Scientific Director of The Cancer Research Campaign, Dr Trevor Hince, says: “Prof Kinlen first put forward this theory in 1988 and since then more than ten scientific papers,** many of them Campaign-funded, have helped support it.  Sir Richard’s comments now give a ringing endorsement of Leo’s and The Campaign’s work.”

Since the 1950s, there has been a ten-fold excess of two  cancers - acute lymphoblastic leukaemia (ALL) and the related disease Non-Hodgkin’s lymphoma (NHL) - among children living in Seascale near Sellafield.

A Government committee, set up to investigate the phenomenon, ruled in 1984 that there was no evidence to show the cases were linked to radiation from the nearby Sellafield nuclear power station.

Now Dr Heather Dickinson and Dr Louise Parker of Newcastle University’s Child Health Dept say their work shows the Seascale cluster could have been predicted because of the amount of population mixing going on in the area.

It also shows that in Cumbria around half of all cases of ALL and NHL could be linked to an infection resulting from population mixing.

Their findings come from a detailed study of records of 119,539 children born in Cumbria (excluding Seascale) between 1969 and 1989.

These children were followed up to see whether those who went on to develop ALL or NHL had anything in common.

Strikingly, researchers discovered that children were much more likely to develop one of the two diseases if both their parents were born outside Cumbria.

They also discovered that children were considerably more at risk if they were born into an area where a higher than average number of  residents were newcomers or people born outside Cumbria.

Dr Dickinson and Dr Parker then devised a statistical model, using these findings, to see whether they could accurately predict the number of cases of ALL and NHL among children in Seascale.

From 1950 to 1989, there were six cases of ALL/NHL in children born in Seascale and two cases among children who moved to the village when they were young.  And, allowing for chance variation, their model correctly predicted these numbers.

Dr Dickinson says: “Our study shows that population mixing can account for the Seascale leukaemia cluster and that all children , whether their parents are incomers or locals, are at a higher risk if they are born in an area of high population mixing. But children of incomers, who are in the minority, seem particularly at risk because they are potentially being exposed to more new infections.”

Prof Kinlen of Oxford University says: “The latest findings are gratifying and give confirmation of infection as a cause of childhood leukaemia more generally, not just at Seascale.  The challenge now facing researchers is to identify the infective agent and at the moment scientists have little idea what it could be.”

Acute lymphoblastic leukaemia (ALL) is a type of leukaemia (a cancer of the white blood cells). There are around 320 new cases of ALL in UK children every year and it is the commonest childhood cancer. Non Hodgkin’s lymphoma (NHL) is a cancer of the lymph glands. There are around 70 new cases of NHL in UK children every year.

*British Journal of Cancer: Vol 81, issue 1, Sept 1999
**These papers investigate urban-rural mixing in a variety of situations including rural new towns and the North sea oil industry in Northern Scotland.