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COMARE 7th Report: Parental Radiation Exposure and Childhood Cancer

The balance of evidence indicates that rates of cancer in the children of male radiation workers in the British nuclear industry are not related to parental radiation exposures. This is the conclusion of the 7th COMARE Report published today (15 August 2002). The report follows an extensive review of the most recent epidemiological studies of the offspring of radiation workers and also the latest laboratory and genetic research relating to the possible biological mechanisms which could explain any observed effects in the offspring of irradiated parents. COMARE also noted that although some recent studies suggest that the children of male radiation workers are more likely than other children to develop childhood leukaemia or non-Hodgkin's lymphoma (NHL), similar findings have been found in other industries.

The key findings in COMARE's review, which led to this conclusion are:

  • Studies in the UK or in other countries have found no evidence of a causal link between workers' exposure to radiation and cancer in their children.
  • There is a known "cluster" of childhood cancer in the village of Seascale near to Sellafield where the fathers of children who developed leukaemia or non-Hodgkin lymphoma had all received larger than average occupational radiation doses. However, COMARE have noted that no excess was found in the surrounding area where the majority of radiation workers lived. If there were a link with workers' radiation exposure, similar rates of cancer would have been expected in their children.
  • Childhood leukaemia accounts for just under half of the cases of cancer in young people in Seascale in the last 50 years. This makes it increasingly unlikely that a single factor, such as parental exposure to radiation, is the cause.
  • Much of the increased rate in Seascale may be due to some effect associated with population mixing, probably an increased exposure to infectious agents. Although it is possible that this effect might combine with parental radiation exposure to give a greater risk, it is more likely that it is just a chance happening that the highest paternal doses may have occurred just when the population mixing effect was at its greatest.

COMARE also highlight that:

  • The risk of the children of radiation workers developing childhood leukaemia, in absolute terms, is low.

COMARE have recommended that more basic research is needed into the underlying changes in the genetic code of cells which leads to the development of childhood cancer. The research emphasis must not focus solely on radiation as many other agents may bring about these genetic changes. Government has accepted these recommendations. Further work has already been commissioned.)

Press Enquiries: Please contact Professor Bryn Bridges (01273-877515)

Notes for Editors

In 1990, Professor Martin Gardner and his colleagues in Southampton published a report, funded by the Department of Health and the Medical Research Council, into the factors that could be relevant to the development of leukaemia and lymphoma in young people living in West Cumbria. This study concluded that the raised incidence of leukaemia and non-Hodgkin's Lymphoma (NHL) among children living near to Sellafield nuclear installation was associated with the parental employment and recorded external dose of whole body radiation during work at the plant prior to conception of an affected child. The result suggested an effect of ionising radiation on fathers that may be leukaemogenic in their offspring, although other, less likely, explanations were possible. A subsequent Health and Safety case control study found a similar result but was based mainly on the same cases in the Gardner report. The association was confined to workers who started work at the plant before 1965 and who were resident in the village of Seascale at the time of their child's birth.

At the request of the Department of Health and the Health and Safety Executive COMARE has carried out a comprehensive review of epidemiological studies of the offspring of radiation workers in the UK and in other countries. Three recent studies of radiation workers in the UK and one study in Germany suggest that the children of male radiation workers are about twice as likely as other children to develop childhood leukaemia or non-Hodgkin's lymphoma (NHL). This risk is not related to the dose of radiation received by the fathers before conception of the child; it does not achieve statistical significance in all studies and is small in absolute terms. For example, the average risk to all children in the UK by age 15 is about 1 in 1540, and the risk to children of male radiation workers is estimated to be 1 in 840. COMARE notes that the Nuclear Industry Family Study (NIFS) published in 2000 did not detect any significant increase in leukaemia or any other cancer in children born to nuclear industry employees since 1965. Professor Gardner (1990) found similar excess risks in other industries (farming, chemical industry and the iron and steel industry), and the findings may be related to other factors including the fact that working populations are often socially different from the general population.

When examining small increases in risks appearing in epidemiological studies, there is always a possibility that associations can be due to chance or to some confounding factor. Currently there is no clear scientific understanding of all of the stages involved in the development of leukaemia. For example, it appears that childhood leukaemia is more prevalent in families from higher social class backgrounds. One hypothesis suggests that such children will be less likely to be exposed to common infections and therefore their more protected immune system will be more susceptible to viral agents that might induce changes that lead to leukaemia.

Another hypothesis is that exposure to infectious agents brought about by migration and population mixing may cause an excess of childhood leukaemia. However, while there is considerable epidemiological evidence consistent with these hypotheses there are no proven biological mechanisms to back them up. COMARE is attempting to address some of these complex issues in its report on the geographical distribution of childhood cancer in Great Britain in the last thirty years or so. This report is in preparation.

Regarding the cluster of cases near Sellafield, COMARE concluded it is possible that population mixing could be responsible for a substantial part of the excess of childhood leukaemia and NHL. Furthermore COMARE noted that it is only in Seascale that a significant association of childhood leukaemia and NHL with paternal preconception exposure is consistently reported. However, the most recent analysis of these data suggests a much weaker association and the Committee concludes that care must be exercised in the interpretation of these studies that are based on very small numbers. Other studies in the UK and from around the world have found no evidence for an association between childhood leukaemia and NHL and paternal preconception exposure. The excess cases were primarily seen between 1950 and 1970 in Seascale, and not in other more distant towns where the majority of Sellafield nuclear workers lived. COMARE says it is possible that the apparent dose related response in Seascale could be due to confounding, ie, there could be an unsuspected linkage between paternal dose and population mixing, or whatever this is a surrogate for. However, the Committee cannot exclude the possibility that there was some factor associated with Seascale in the 1950s and 1960s that interacted synergistically with an effect of radiation that would otherwise not have been noticeable.

Finally, COMARE conclude that the Seascale "cluster" is not simple; one third of the cases are of cancers other than leukaemia and non-Hodgkin's lymphoma, for which some relation to paternal radiation dose was proposed by Professor Martin Gardner. They also note that leukaemias, for which a population mixing hypothesis has been proposed by Professor Leo Kinlen, constitute less than half the cases.

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