Science and history solve the mystery of the cancer clusters

IT BEGAN in 1983 with an emotionally charged television documentary - Yorkshire TV's Windscale: the Nuclear Laundry - which for the first time highlighted a disturbingly high rate of childhood leukaemias near Britain's nuclear reprocessing plant, later to be renamed Sellafield.

The programme concentrated on the concerns of local doctors who noticed exceedingly rare blood cancer in children was more common in their district. It became known as the Sellafield leukaemia cluster. The public outcry following the programme forced the Government to establish an official investigation led by Sir Douglas Black, the eminent medical scientist and former president of the Royal College of Physicians.

His committee concentrated on the high incidence of childhood leukaemia in Seascale, the village nearest the Sellafield plant and the place where many nuclear workers and their families lived. Doctors had reported seven cases of leukaemia in people under the age of 25 who had lived in the town between 1955 and 1983. For children under the age of 10, the "excess" number of leukaemias was estimated to be 10 times the national average - five cases against 0.5 expected. Although each case was a deep family tragedy, the actual number was still small. But the cluster was so significant against the national level that the Black committee could not disregard its potential importance, particularly with the fears over radioactive emissions from Sellafield.

An exhaustive inquiry into radiation emissions by the Black committee failed to establish them as the cause of the children's cancers. On what was then known about the level needed to trigger a cancer, the Black committee found the known emissions from Sellafield were far too small to account for the leukaemia cluster.

But many ordinary people were not convinced. A coalition of green activists, anti-nuclear groups, the local authority and families of affected children suggested a cover-up and lobbied hard for a deeper inquiry.

One of the Black committee's major recommendations was the setting up of a "designated body with significant health representation to enable decisions on action with regard to the control of permitted radioactive discharges to take account of all relevant factors".

Out of this came the Committee on the Medical Aspects of Radiation in the Environment (Comare), a powerful body of experts who were to undertake exhaustive and long-term investigation into all aspects of radioactivity and ill health. Over the next 13 years, Comare produced four in-depth reports. Its first was highly critical of the failure of British Nuclear Fuels Ltd (BANFF), the operators of Sellafield, to declare discharges of uranium oxide particles into the Irish Sea. Then the Irish government became concerned, leading to intense pressure to reduce Sellafield's emissions further.

Comare widened its investigations to other nuclear sites, including Dounreay in northern Scotland and the nearby community at Thurso, and the atomic weapons plants at Aldermaston and Burghfield in Berkshire. A further Yorkshire TV documentary - Inside Britain's Bomb - in 1985, found a second cancer cluster near the latter two run by the Ministry of Defence, based on information from doctors at the Royal Berkshire Hospital.

Comare confirmed higher levels of leukaemias near Dounreay and, to a lesser extent, near the atomic weapons factories, but failed to establish a clear link with radioactive emissions. Again there was just not enough radioactivity released into the environment to account for the cancer clusters.Comare investigated many avenues. Was it the unusual social mix of people around Sellafield (whose local population has the highest level of professionals in the country)? Or could it be exposure to chemicals, or some unknown factor? Radiation could still not be ruled out. Perhaps the inhabitants of Sellafield were being exposed to higher than expected levels of radioactivity by some unknown route?

One unusual idea was championed by Professor Leo Kinlen, an epidemiologist at Oxford University, funded by the Cancer Research Campaign. He suggested an unknown infection - possibly a virus - might be responsible for the clusters. Professor Kinlen based his hypothesis on the history of infectious epidemics and the importance of the mass movement of people and the density of population centres.

He believed the leukaemia cluster around Sellafield was the result of a mass influx of people over many years who had brought infections with them which had resulted in cancer for a few children. Some cancers can be induced by a virus. Leukaemia in cats is caused by feline leukaemia virus and Burkitt's lymphoma was the first human malignancy linked with an infectious virus. For more than 10 years, Professor Kinlen built up substantial evidence. He showed:

nIn the First World War camps, American soldiers from sparsely populated states were more prone to infections than city dwellers.

nChildhood leukaemia was higher in populations subjected to large-scale mixing, such as the wartime evacuation of urban children to rural areas.

nCancer clusters appearing in other instances of population mixing, say, the creation of new towns, the influx of oil workers into Scotland and rural regions subjected to a significant rise in urban commuting. But it was the professor's investigation of the Seascale cluster that began to convince the sceptics. The isolated village, 37 miles from the nearest town and between the Lake District and the Irish Sea, made it an effective cul-de-sac, he said. This area was subjected to a huge influx of people over 50 years, nuclear staff and the thousands of construction workers who built the plant.

Professor Kinlen said: "Half the children born in the village had moved away before reaching school age; half of those born elsewhere who attended the Seascale primary school had moved before the age of 11. These movements resulted in an unusually high level of contacts, particularly for children who did not move."

He concluded the cancer cluster was the result of population mixing introducing a mysterious cancer-causing agent to susceptible children.

He said in 1995: "The findings point strongly to the transmission of some (unidentified, possibly viral) infection(s) in the causation of this disorder and they provide the most likely explanation for the excesses near Sellafield."

Professor Kinlen's once-controversial idea has now become the established cause of childhood leukaemia.