National Public Health Service for Wales Childhood Cancer Incidence – Gwynedd & Anglesey, North Wales
Childhood Cancer Incidence – Gwynedd & Anglesey, North Wales
Discussion report by the National Public Health Service for Wales
Version:9 Date:09/03/2005 Status: Final Author: Andrew Jones. Environmental Page: 1 of 18 Public Health Team National Public Health Service for Wales Childhood Cancer Incidence – Gwynedd & Anglesey, North Wales
Executive Summary
Background and context
In February 2004 the alleged existence of an increased risk of childhood cancers in areas of the North Wales coastline, linked to radiation discharges from the nuclear installation at Sellafield in Cumbria, was reported through the media.
The media reports followed analysis of information and the subsequent release of a report by an organisation known as ‘Green Audit’. Having compared information from different sources for the period 1982-1990 and 2000-2003, the ‘Green Audit’ report claimed to identify evidence of a continuing increased risk of childhood leukaemia and other childhood cancers (brain/spinal and retinoblastoma) in the population living close to the Menai Straits.
The National Public Health Service for Wales (NPHS) was asked to support the Local Health Boards in Gwynedd and Anglesey in investigating these latest claims. The NPHS requested the Welsh Cancer Intelligence and Surveillance Unit (WCISU) to examine relevant validated cancer registry information and then separately reviewed the findings, together with those released by ‘Green Audit’.
This report summarises the findings of the NPHS review. WCISU have prepared a separate report which includes details of the technical analysis and tables of results.
It should be noted that the issues raised by the ‘Green Audit’ report are not new. Similar claims in relation to the North Wales coast have been made previously by ‘Green Audit’. These previous claims have been thoroughly investigated by an independent expert advisory committee – the Committee on Medical Aspects of Radiation in the Environment (COMARE) as recently as 1999. No evidence was found to support allegations of increased risk of childhood cancers close to the North Wales coastline. A public statement has previously been made by COMARE to this effect. This conclusion has also been supported by a complete analysis which was published in 2001.
Methodology and Limitations
These latest claims made by ‘Green Audit’ have been investigated by examining validated cancer registry information. Where possible the methodology described in the ‘Green Audit’ report has been followed. In addition cancer registry data has been examined for the whole 22 year period 1982-2003.
The NPHS wishes to highlight that there are limitations to undertaking studies on small geographical areas, which must be reflected in the methodology used and subsequent interpretation of results. Data accuracy is paramount when undertaking small area studies. The NPHS has been advised that in investigating this issue,
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WCISU has worked closely with the clinicians who treat children with cancer, so as to ensure that the data which has been used is as accurate as possible. The NPHS acknowledges that cancer registration is a dynamic process and that it can take several years for incidence rates to stabilise.
Childhood cancer is relatively rare. WCISU and NPHS operate under strict legal and ethical guidelines which prevent the disclosure of information which may break patient confidentiality. For this reason the NPHS report does not contain details of the statistical data which has been analysed by WCISU.
It is also difficult to comment in detail publicly on the findings of the ‘Green Audit’ report, as this relates to small populations and very small numbers of cases.
Results and Conclusions
The NPHS has reviewed the statistical analysis undertaken by WCISU to date. Following analysis of the cancer registry information for the period 1982–2003, no credible evidence has been found to support the findings of an increased risk of childhood cancer in the Menai Straits/Caernarfon area of North Wales as claimed in the ‘Green Audit’ report.
A continuing trend of increased incidence of childhood leukaemia has not been demonstrated during the period. Similarly, rates for brain (and spinal) tumours and retinoblastoma in children within the study areas have not been found to be significantly different from expected.
Weak evidence for a slightly raised risk of childhood leukaemia in the study areas has been found in the 2000-2003 period. This is however based on a very small number of cases, notably in relation to the smaller of the two study areas. This is not apparent in any previous period and is most likely a chance finding.
No significant results have been found for childhood leukaemia in either the Anglesey or Gwynedd LHB populations for the 2000-2003 period or any previous period.
NPHS and WCISU can see no reason for public concern in respect of this latest ‘Green Audit’ report.
NPHS will continue to work with WCISU and other partners in the surveillance of LHB populations across Wales. Any unusual occurrences of cancer will be brought to the attention of the NPHS as a matter of routine.
Additional Comments
The NPHS wishes to point out that there are many limitations associated with studies based on small areas of population and great care is required in undertaking analysis and interpretation of results. Errors in the methodology, analysis and interpretation of results have been found whilst undertaking the review of the ‘Green Audit’ report. The
Version:9 Date:09/03/2005 Status: Final Author: Andrew Jones. Environmental Page: 3 of 18 Public Health Team National Public Health Service for Wales Childhood Cancer Incidence – Gwynedd & Anglesey, North Wales report is based upon very small numbers of cases and appears to overestimate the level of risk and the statistical significance of results leading to the potential for unnecessary public concern.
The NPHS strongly recommends that all organisations adopt accepted procedures and processes for ethical approval and scientific peer review, prior to carrying out studies and releasing information to the public. Such processes are essential in ensuring that errors/ deficiencies in study design/methodology/interpretation are identified prior to publication. The NPHS is aware that ‘Green Audit’ have previously received such a recommendation from COMARE following reviews of previous reports.
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1. Background
In February 2004, televisioni and newspaperii reports appeared in the Welsh media referring to the existence of a ‘cluster’ of childhood cancers (leukaemia, brain cancer and retinoblastoma) along a section of the North Wales coastline and linking them to radiation releases from the Sellafield nuclear reprocessing plant in Cumbria.
The reports followed investigation by media researchers and subsequent analysis of information and production of a reportiii by the organisation ‘Green Audit’. The NPHS wishes to point out that the methods used in this report do not appear to have been subject to ethical approval, and there was apparent no peer review process undertaken prior to the release of information into the public domains
Following the initial allegations, a press release was issued by the Welsh Cancer Intelligence and Surveillance Unit (WCISU) (Appendix 1), which made clear that the questions raised by the report were not new and that investigations to date by WCISU and the Committee on Medical Aspects of Radiation in the Environment (COMARE) had not yet found any significant support for similar claims made previously by ‘Green Audit’.
Following the media coverage, neither Gwynedd nor Anglesey Local Health Board reported receiving any requests for information from local communities.
The Welsh Assembly Government, on receiving correspondence from the local Assembly Member for Caernarfon, requested the National Public Health Service for Wales to assist the Local Health Boards of Gwynedd and Anglesey by coordinating a response to the alleged findings.
This short discussion document puts the subject in context and summarises the action taken to date.
2. Context
Claims of increased childhood cancer incidence in North Wales are not new. A report previously released by ‘Green Audit’ made similar claims of increased childhood cancer risks across the North Wales coast. This reportiv, together with a report prepared by WCISUv (which did not support such conclusions), were reviewed by COMARE, who issued a statementvi concluding that they had found no evidence to support the contention that there was an increased incidence of childhood leukaemia or other cancers close to the North Wales Coast. This conclusion was supported by a complete analysis, which was published by Steward et al vii in 2001.
The COMARE statement concluded that ‘Green Audit’ had used incorrect data and requested the authors to withdraw the conclusions of the analysis, which had given rise to considerable public concern.
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The NPHS notes that the COMARE website also contains other COMARE public statementsviii, which are very critical of similar reports prepared by ‘Green Audit’ across the UK and cast severe doubt over the scientific value of such reports. The statements have also previously recommended that ‘Green Audit’ should follow normal scientific practice and submit their reports for peer review, rather than releasing their reports themselves without such review.
3. ‘Green Audit’ report on Childhood Cancer in North Wales 20043
The ‘Green Audit’ report (available from the website of the Low Level Radiation Campaign http://www.llrc.org) makes a number of claims concerning high risks of certain childhood cancers in North Wales. Part 1 of the report makes reference to previous work carried out by ‘Green Audit’ on downloads of tabulated data received from the former Wales Cancer Registry in 1996 covering the period 1982-1990. In part 2 of the report, data collected by media researchers concerning current cases are introduced, analysed and discussed in parts 3 to 5. Interpretation of this analysis by ‘Green Audit’ suggests high relative risks for cancer in children aged 0-4 years and 0-14 years, mainly for leukaemia and brain tumours and living within the coastal towns near the Menai Strait. A hypothesis is proposed suggesting that these increased risks are attributable to exposure of the population around the Menai Straits to contamination originating from the nuclear reprocessing plant at Sellafield, which has accumulated in the mudflats around Bangor. Additional commentary on the analysis also appears in a ‘Briefing for Activists’ on the website of the Low Level Radiation Campaign.
The Green Audit report claims a number of main findings, which it uses to rule out the existence of a ‘random cluster’ and provide evidence of an environmental effect:
• ‘A Relative Risk of 28 (also described as a 28 fold excess) for childhood leukaemia (ages 0-4) in Caernarfon over the period ‘2000-2003’ (page 6 of report and page 1 of ‘Briefing for Activists’ refers) • A previous high rate of leukaemia in the same area between 1982-1990, (suggesting a continuing trend) ( p6 of report refers) • Large excess risk of brain tumours in children in the same town (p6 of report refers) • The existence of cases of retinoblastoma in the same area (p.9 of report refers)
It should be noted that the report and supporting information also make statements which cast doubt on the integrity and scientific rigour of national bodies, such as COMARE, the National Radiological Protection Board (NRPB) and cancer registries, and recommends police investigation into alleged losses of data from cancer registries. The NPHS wishes to point out that similar issues have already been investigated by COMARE and responses refuting such allegations are reported in statements on the COMARE website (http://www.comare.org.uk).
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4. The Approach of the National Public Health Service for Wales.
In supporting the Local Health Boards for Gwynedd and Anglesey, the NPHS has concentrated its enquiry on the factual evidence to support the allegation of a previously undetected cancer cluster. The NPHS has independently reviewed the analysis undertaken to date by the Welsh Cancer Intelligence and Surveillance Unit (who have themselves undertaken detailed analysis of relevant cancer registry information from an objective and independent perspective).
Other issues in the ‘Green Audit’ report, such as the hypothesis of a coastal effect on childhood cancer in Wales, have, as summarised above, already been examined thoroughly by a peer reviewed study, which has found no evidence of the alleged effect.
5. Small area study limitations
NPHS wishes to make clear the limitations of using small area studies in isolation to investigate a suspected cancer cluster.
Firstly, comparing observed and expected cases is problematic when investigating small numbersix. The expected number of cases may only be a small decimal figure (less than one), whereas the observed cases are constrained to be a whole number. For example, if only one case every 30 years is expected (0.2 cases in a six year period), but one case occurs in the 6 year period of study, the incidence rate equals 5. However it would be misleading to interpret this as a cancer incidence five times higher than expected.
Secondly, the use of Poisson significance tests is widely regarded as insufficient when dealing with very small numbers of cases and this has been discussed in the context of radiation exposurex. A small variation of one or two cases can produce a disproportionately large effect on the incidence rate and its apparent statistical significance.
Thirdly, when presenting rate ratios it is usual to give confidence intervals alongside. Confidence intervals demonstrate the uncertainty in point estimates of rate ratios based on small numbers, although there are still severe limitations of interpretationxi. P values can be particularly misleading and the overuse or rather the misuse of arbitrary cut - off levels is not recommended in modern statistical practice.xii
Fourthly, in order to apply any tests of statistical inference, certain assumptions have to be met as regards the sample. The proper practice is to state the hypothesis before one has collected or analysed the data (‘a priori’). However, if a researcher only declares the hypothesis after having seen the empirical evidence (‘a posteriori’), this is inappropriate and is closely related to data dredging (which means exploring various different ways the data can be analysed and presented in order to select the particular way of presentation that gives the maximum impression of an effect). In such cases, the p values obtained are rendered uninterpretablexii..
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In addition to these issues, childhood cancer is relatively rare. This means that in small area studies of this nature, the number of cases will be extremely small. Data accuracy is therefore of paramount importance. Cancer registries such as WCISU routinely validate cases with treating clinicians.
6. Data Confidentiality
Cancer registries (and their partners) have a legal obligation to protect data which could potentially be used to identify an individual. The UK Association of Cancer Registries (UKACR) and the Department of Health have issued guidelines to ensure that registries remain clearly within the bounds of legal requirements. UKACR follow the Patient Information Advisory Group (PIAG) agreed data release proceduresxiii.
WCISU have advised that therefore they are not able to release data in the public domain pertaining to a population of fewer than 1000 or very small absolute numbers of cases, so as to protect patient confidentiality. For this reason the NPHS report does not include details of the data analysed by WCISU. It is understood that WCISU have taken advice in relation to the release of this data into the public domain.
It is also difficult to comment in detail on reports, such as that released by ‘Green Audit’, without breaching patient confidentiality. However WCISU have discussed all relevant details with NPHS to enable NPHS to discharge the duty of public protection.
7. Childhood Cancer Incidence in the Anglesey & Gwynedd LHB
The ‘Green Audit’ report concerns itself with two datasets covering different time periods and collected in different ways: a) a download of data received in 1996 from the former Wales Cancer Registry covering 1982-1990 aggregated to OPCS Areas of Residence b) the results of an informal survey, apparently conducted by media researchers, of parents/relations of childhood cancer patients being treated at Alder Hey hospital, Liverpool covering 1996-2003, using so called “snowball” sampling. (Snowball or reputational sampling has been defined as a technique for finding research subjectsxiv. One subject gives the researcher the name of another subject, who in turn provides the name of a third, and so on. Literature indicates that such methodology is most often used in social research to reach ‘hard to reach’ or ‘hidden’ populationsxv.
In investigating the claims made by the ‘Green Audit’ report, the NPHS requested WCISU to undertake investigation of relevant cancer registry data so as to:
• Repeat (as far as possible) the methodology used by ‘Green Audit’ (acknowledging relevant limitations) • Examine any trends for childhood leukaemia within the study area between 1982 and 2003
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• Provide information on childhood leukaemia within the populations of Anglesey and Gwynedd LHB for the period 2000-2003 and previous periods.
To undertake this, it is understood that WCISU used data from the Wales Cancer Registry (WCR) frozen file (as of 1996) to produce tables regarding 1982-1990 to compare with those released by ‘Green Audit’. Data for the period 1996-2003 has been extracted from the current database held at WCISU to obtain the most current and accurate data as possible. With help from clinical colleagues, data validation officers have attempted to locate and validate all cases of childhood cancer in Wales up to the end of 2003. The basic format of the ‘Green Audit’ report was followed.
8. Childhood Leukaemia (ICD10 codes C91-C95) ages 0-4 for the period 1982-1990
This was referred to in Table 1 (page 2) of the ‘Green Audit’ report with specific reference made to Bangor and Caernarfon. This data is population based and a frozen database file produced by WCR in 1996 has allowed WCISU to reproduce the analysis.
The WCISU calculations used population figures from the 1971 census Area of Residence (AOR) to calculate the Relative Risk (RR) and the overall rate for 0-4 years in Wales for the period as an external standard to calculate expected figures for the AOR in question.
Comparison of WCISU results with ‘Green Audit’ show smaller relative risks and no statistically significant results being found in the WCISU study. In addition, WCISU calculated 95% confidence intervals (absent from the ‘Green Audit’ study), which show the wide range of uncertainty which results from using such very small numbers. The very small number of observed cases has led inevitably to sample fluctuation indicated by very wide confidence intervals.
Incorrect analysis and interpretation by ‘Green Audit’ appears to have inflated the risks so that they appear dramatic and alarming.
9. Analysis of information 1996 – 2003
Analysis in the ‘Green Audit’ report (which focuses on the period 2000-2003 for leukaemia and 1996-2003 for other cancers) is reportedly based on (numerator) data provided for the organisation by media researchers. The information appears to have resulted from a reporter investigating cancer services for North Wales children at Alder Hey hospital, who carried out some form of ‘snowball’ sampling. Details are presumably based on anecdotal reports from parents, and relatives. Incidence figures reported are analysed using the annual rate for England and Wales for 1997. Two study areas were used in the ‘Green Audit’ study. The first ‘Menai’ (to include all electoral wards with a boundary to the sea or with half the area within 10km of the coast) and the second ‘Caernarfon’ (a subset of 4 wards included within the larger study area).
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The methodology described in the ‘Green Audit’ report has been followed by WCISU.
The NPHS notes that the data relating to ‘cases’ displayed in the ‘Green Audit’ report appears incomplete (e.g. tables 3 and 7 in relation to age/age at diagnosis)
In repeating the analysis, WCISU has used similar electoral ward boundaries (denominator populations) identified in the ‘Green Audit’ report. NPHS notes that in repeating this analysis confusion/inconsistency in ward identity in the ‘Green Audit’ report was highlighted. The NPHS also notes with concern that some wards, which appear to fit the inclusion criteria described by ‘Green Audit’, do not appear to be included in the larger study area subsequently used in the ‘Green Audit’ analysis.
When undertaking small area analysis data accuracy for both cases (numerator) and populations (denominator) is paramount.
For their analysis, WCISU has used population based numerator data from the cancer registry database, which have been validated by clinical records held by clinicians. This included the urgent transfer of validated data from the Mersey and Cheshire Cancer Registry, in which area Alder Hey, the treating hospital for most children in North Wales with cancer, resides.
Relevant data from cancer registry records for years 1982-2003 inclusive have been used by WCISU to ensure complete examination for the whole period.
Incidence figures have been analysed using the appropriate/equivalent Wales rate for both the 2000-2003 period and other periods studied, as is the WCISU usual practice.
Data for each LHB area for 2000-2003 and previous periods have also been examined, notably as most of the Anglesey wards are adjacent to or in close proximity to the coast.
Figure 1: Identification of the Menai wards Figure 2: Identification of Caernarfon wards Menai Wards (1991 Census) – Caernarfon Wards (1991 Census) 10km of the Menai Strait
Code 1991 ID 1991 Ward Name 27 1 SZFA Bethel 2 SZFB Bontnewydd 29 3 SZFC Cadnant 4 SZFD Deiniol 34 5 SZFE Deiniolen 31 7 11 30 17 6 SZFF Dewi 28 4 16 9 10 7 SZFG Garth 6 13 8SZFHGerlan 9SZFJGlyder 32 22 10 SZFK Hendre Code 1991 ID 1991 Ward Name 23 11 SZFL Hirael 19 1 SZFX Menai Caernarfon 26 1 12 SZFP Llandigai 33 8 13 SZFQ Llanllechid/Aber 1 2 SZFC Cadnant 12 2 14 SZFS Llanrug 3 SZFZ Peblig 21 3 18 15 SZFT Llanwnda 4 SZGG Waunfawr 3 16 SZFU Marchog 20 14 17 SZFW Menai Bangor 24 5 4 18 SZFX Menai Caernarfon
2 19 SZFY Ogwen 20 SZFZ Peblig
15 25 21 SZGA Penisarwaun 22 SZGB Pentir 23 SZGD Rachub 24 SZGE Seiont 25 SZGG Waunfawr 26 SZGH Y Felinheli 27 TCFC Beaumaris 28 TCFH Cadnant 29 TCFK Cwm Cadnant 30 TCFU Llanfair Pwll 31 TCFX Llanfihangel Ysgeifiog 32 TCFZ Llanidan 33 TCGK Rhosyr 34 TCGN Tysilio
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10. Childhood Leukaemia in Caernarfon and in wards near the Menai Strait, ages 0-4 and 0-14 years for the period 1982 -2003 ( ICD10 codes C91-C95)
In repeating the exercise a number of fundamental errors were noted in the ‘Green Audit’ methodology. Details of these are as follows:
• Incorrect calculation and interpretation of expected values and relative risk (notably the headline relative risk of 28 for childhood leukaemia between 2000- 2003, which in addition to being based on very small numbers of cases and being described as a ‘28 fold increase’, also appears to involve the use of 3 years expected counts but 4 years observed counts) • Use of unconventional risk estimates acknowledging lack of data accuracy ( e.g. page 9 Green Audit report) • Using p values with small counts • No use of confidence intervals • Potential confusion over ward geography and geographical analysis (e.g. inconsistency in wards identified when repeating analysis using the names and codes referenced in the ‘Green Audit’ report). • Errors in population counts and figures • Errors in expected counts • Evidence of data dredging (e.g. the change of the conventional 0-14 age band to 0-15 age band when analysing data on brain and spinal tumours, page 8 Green Audit report).
The NPHS notes that errors have been previously documented following the review of other ‘Green Audit’ reports.xvi
Analysis of information 1982 -2003 by WCISU for childhood leukaemia (0-4 and 0-14 age bands) using a range of year band periods, does not show any credible evidence of an increased risk of childhood leukaemia or an increasing trend over time in either study area. For the twenty two year period, it should be noted that the number of cases of childhood leukaemia in the smaller study area (Caernarfon ward subset) were very small indeed.
Within the most recent period 2000-2003, WCISU report weak evidence for a possibly raised incidence of childhood leukaemia. This is based on a very small number of cases, notably in relation to the smaller (Caernarfon ward subset) study area. As described above, the effect does not appear to be apparent in any previous period and is most likely a chance finding.
WCISU have also reported risks for childhood leukaemia in relation to the Anglesey LHB and Gwynedd LHB populations. No significant results were obtained for the period 2000-03 or any previous period for either LHB population. These LHB results are similarly based on very small numbers of observed cases and are subsequently accompanied by very wide confidence intervals. It should also be noted that within the 2000-03 period, additional WCISU analysis has identified other LHB areas in Wales which experienced higher crude rates for childhood leukaemia.
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11. Brain and spinal tumours in children 0-14 in the Menai area 1996-2003 (See Appendix 2 for ICD10 codes)
It was not clear from their report whether Green Audit analysed malignant and benign tumours, which is usual practice, or just malignant tumours.
NPHS therefore requested WCISU to report on both categories of tumours.
Again cases of such childhood cancer in the period were very small. WCISU analysis shows no evidence of raised relative risk. In respect of Caernarfon, WCISU found no case of malignant cancer recorded during the period.
12. Retinoblastoma (ICD code 692), ages 0-14 years for the period 1994-2003
WCISU reported on the incidence of retinoblastoma in Wales and North West Wales. No results were found to be significant. WCISU report no cases of this condition were recorded for Anglesey LHB area during the ten year period. Again very small numbers of cases are involved over the ten year period. An increase or decrease in just one case will greatly affect the relative risks.
13. Discussion
The report on which the media reports were based appears to have been produced by a campaign group, who have claimed on a number of previous occasions to have uncovered evidence to demonstrate that low level radioactive discharges from nuclear facilities have led to increased levels of cancer in Wales and elsewhere in the UK.
Previous investigations by cancer registries and consideration by UK expert advisory bodies, such as COMARE, have revealed data errors and methodological flaws in previous reports produced by ‘Green Audit’ (refer to COMARE website for detail). Previous requests have been made by COMARE to ‘Green Audit’ to submit study work for ethical and peer approval of methodology and peer review assessment prior to the release of information to the public, as failure to do so can give rise to unnecessary public concern. The scientific value of previous Green Audit reports has been evaluated as low by COMARE.
Errors in methodology, analysis and interpretation have again been observed in this ‘Green Audit’ report, which appear to have inflated risks with the potential for public concern.
Other issues alleged in the report e.g. hypothesis of a coastal effect on childhood cancer in Wales and the unconventional risk estimates used by Green Audit, have been previously discussed and rejected by the expert advisory group COMARE.
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In undertaking small area studies of this nature, data accuracy is paramount. Whilst the data used in the first part of the ‘Green Audit’ report was supplied by the cancer registry, the remainder of the data used by ‘Green Audit’ appears to have originated from the collection of self reported information from parents, relatives or carers of children receiving cancer services. The collection of anecdotal medical reports by lay persons is a notoriously error prone process. Other studies have shown that self reported diagnoses are frequently inaccurate. The population at risk and details of observed cases are also unclear in the ‘Green Audit’ report. To illustrate this point, there appear to be internal inconsistencies in the dates/ages displayed in tables in the ‘Green Audit’ report (e.g. table 2) and other tables containing information on observed cases are clearly incomplete (tables 3 and 7).
The use of validated cancer registration data, as used by WCISU, has been assessed as much more reliable. The additional work carried out by WCISU to validate and collate the childhood cases up to the end of 2003, and the assistance of the clinicians who treat the children, will have further ensured the accuracy of the data used.
The WCISU analysis reports no evidence to support the conclusions of the ‘Green Audit’ report.
In relation to the main points raised by the ‘Green Audit’ report, it is apparent that the headline Relative Risk of 28 during the period 2000-2003 appears to be the result of incorrect analysis and interpretation.
The original findings of a previous ‘Green Audit’ study, which is referenced to evidence a trend of increased risk in relation to the coastline, have previously been subject to review by the relevant expert advisory group COMARE who found them to be grossly inaccurate and requested ‘Green Audit' to withdraw the report from their website. Furthermore analysis of childhood leukaemia incidence over the same period (1982 – 1990) using the same data set by WCISU shows no evidence of increased risk.
Further analysis of data over the whole period 1982 – 2003 by WCISU shows no credible evidence which suggests an increased risk of childhood leukaemia or an increasing trend.
Weak evidence of a possibly raised incidence of childhood leukaemia in the 2000- 2003 period for the study areas has been reported by WCISU. This is based upon a very small number of cases, is not apparent in any previous period and is not regarded by either NPHS or WCISU as credible evidence of raised risk.
Analysis of data for the Anglesey and Gwynedd LHB populations has not identified any significant results.
It is also widely accepted that simple observed/expected ratios are insufficient evidence to prove or disprove the existence of a cancer cluster in small areas.
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No evidence of a raised relative risk of brain and spinal tumours (referred to on p 6 of the ‘Green Audit’ report as the “strongest evidence of an environmental effect”) was found by WCISU.
No evidence of a raised relative risk for retinoblastoma in children was found by WCISU.
All the analysis has involved very small numbers. The wide confidence intervals demonstrated by the WCISU analysis demonstrates the wide range of uncertainty which results from using such small numbers.
Based on these findings and draft protocols currently being introduced into the NPHS,xvii no further investigation is recommended at this time.
It is very important to note that discussions with both the Anglesey and Gwynedd Local Health Boards have identified that no members of the public have contacted them on this issue either before or after the publication of the ‘Green Audit’ study and subsequent media interest.
The NPHS and WCISU wishes to express concern at the release of reports into the public domain, which have not been subject to usual ethical approval and peer review, and recommend that all organisations, follow approved procedures for ethical approval and peer review of studies. Such processes are essential is ensuring that errors/ deficiencies in study design/methodology/interpretation are identified prior to publication. This echoes views previously expressed by COMARE to ‘Green Audit’.
In taking this issue forward, care is needed so as not to unnecessarily raise levels of public concern.
15. Conclusion
No credible evidence has been demonstrated to support the allegation of increased risks of childhood cancer in the Menai Straits/Caernarfon area of North Wales and NPHS and WCISU can see no reason for public concern in respect of the ‘Green Audit’ report.
The matter of childhood cancer incidence near the coastline of Wales has been thoroughly investigated in a peer-reviewed study published in 2001. No evidence was found for the alleged effect. This has been presented to COMARE who have endorsed its conclusions in a public statement.
NPHS will continue to work with WCISU and other partners in the surveillance of LHB populations across Wales. Any unusual occurrences of cancer detected will be brought to the attention of the NPHS as a matter of routine.
Consideration should be given to referring the ‘Green Audit’ report and WCISU study to the attention of relevant bodies e.g. COMARE for further independent scientific review.
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16. References
i Cancer in North Wales. Y Byd ar Bedwar. S4C. 10th February, 2004 ii Trewyn H. Nuclear link to child leukaemia ‘cluster’. Daily Post. February 10th, 2004 iii Busby C. (2004) Nuclear pollution, childhood leukaemia, retinoblastoma and brain tumours in Gwynedd and Anglesey Wards near the Menai Straites, North Wales 2000 – 2003. Green Audit Report 04/1B; January 2004 (available from http://www.llrc.org last accessed 09/11/2004) iv Busby C, Kocjian B, Mannion E and Scott Cato M (1998). Proximity to the Irish Sea and Leukaemia incidence at ages 0-4 in Wales from 1974-1989. Green Audit Occasional Papers 98/4; August 1998. v Steward J A, Adams Jones D, Beer H and John G (1999). Results of a preliminary study to test the Irish Sea proximity hypothesis of Busby et al. Welsh Cancer Intelligence and Surveillance Unit, Cardiff. March 1999. vi COMARE statement: Childhood leukaemia in Wales (available from http://www.comare.org.uk/statements/comare_statement_wales.htm) vii Steward JA, John G (2001). An ecological investigation of the incidence of cancer n Welsh Children for the period 1985-1994 in relation to residence near the coastline. J.R.Statist. Soc. A; 164:29-43 viii COMARE Press statement 25th November 2003 COMARE statement on Green Audit Occasional paper 2002/5. Cancer in Burnham on Sea: Results of the PCAH( Parents concerned about Hinkley questionnaire) (available from http://www.comare.org.uk/press_releases/comare_pr06.htm ix South West Cancer Intelligence Service (2003). Cancer incidence in Burnham North, Burnham South, Highbridge and Berrow 1990-1999. South West Cancer Intelligence Service. x Gardener MJ (1989). Review of the increases in childhood cancer rates in the vicinity of nuclear installations in UK. J.R Statist.Soc.A:152;307-325(fig2 p313 refers) xi Clayton D, Hills M. (1993) Statistical Models in Epidemiology. Oxford University Press, Oxford (Chapter 12 Small Studies pp110-121 refers) xii Altman DG. ( .) Practical Medical Statistics for Medical Research. Chapman and Hall/CRC London. (Chapter 8 Principles of Statistical Analysis pp. 152-178 refers) xiii http://www.ukacr.org.uk/
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xiv Vogt,W.P (1990). Methodological and Design Issues: Dictionary of Statistics and Methodology: A non technical Guide for the Social Sciences, London: Sage. xv Rowland A, Flint J ( 2001). Accessing Hidden and Hard-to-Reach Populations: Snowball Research Strategies. Social Research Update. Issue 33. University of Surrey. xvi Roberts RJ, Steward JA, John G. (2003) Cement, cancers and clusters: an investigation of an excess cancer risk related to a cement works. J Public Health Medicine 25(4): 351-357. xvii National Public Health Service for Wales (2004). Investigation of an alleged disease cluster when an environmental cause is suggested. Guidance for LDPHs. Draft protocol. National Public Health Service for Wales.
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APPENDIX 1 – WCISU Press Release
Statement from Director of the Welsh Cancer Intelligence & Surveillance Unit for Mr Tweli Griffiths Reporter for “Y Byd ar Bedwar” HTV’s current affairs programme for S4C:
The questions raised by this report are not new and our investigations to date have not yet found any significant support for Dr Busby’s claims. These claims have also been investigated by the COMARE who have made statements to this effect.
As regards this report, some of the analysis 1982-1990 is based upon a download of cancer registry data aggregated to areas now obsolete. These have proved unreliable for this sort of study in the past. The findings presented refer to very small numbers of cases and appear to overestimate the level of risk and the statistical significance.
It is difficult to comment on the analysis of the HTV survey. Cancer registries must protect the confidentiality of their cases. We would need more time for a thorough investigation.
Data accuracy is of course paramount. WCISU work collaboratively with the doctors who actually treat the children to ensure our data is as accurate as possible.
We should point out that childhood cancer is relatively rare and that it can be difficult to produce robust conclusions from sparse data. This is why we feel that the normal scientific peer review process is so important and this should be done before results such as those in the report are released via the media.
Dr John Steward
Director WCISU
14 Cathedral Road
Cardiff
27/02/04
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APPENDIX 2
ICD10 codes used by WCISU for brain and spinal tumours:
Malignant
C70, C71, C72, C793
Benign
D320, D321, D329, D343, D429, D432, D330, D331, D332, D333, D337, D339, D352, D353, D354, D421, D430, D431, D437, D439, D420, D433, D434, D443, D444, D445
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