Childhood leukaemia near nuclear power stations:
Pooled analysis of data from ecological studies in Germany, Great Britain, Switzerland, and France

Background

Following the publication of the German KiKK study [1] of leukaemia in young children in the vicinity of nuclear power stations (NPS), ecological studies were conducted in Germany [2], England [3], Switzerland [4], and France [5]. None of them yielded significantly increased leukaemia rates near NPS with a two-sided test. But the individual studies suffer from low numbers of leukaemia cases in the 5-km zone. In the following, the result of a pooled analysis of the 4 data sets is presented.

Data and Methods

The German KiKK study [1] is a case-control study which cannot be used for a pooled analysis because it does not provide information on expected cases.  But after the KiKK study, an additional geographical study [2] was carried out in the same study region and for the same time span.  The British COMARE 14 report [3] focuses on acute leukaemia plus non-Hodgkin lymphoma but it also contains data for acute leukaemia only.  The Swiss study [4] is a cohort study without numbers of expected cases but these can be calculated from information in the study.  In addition to data on residence at birth, the Swiss study contains data on residence at diagnosis.  The latter are used in the pooled analysis as the other three studies also used residence at diagnosis for determining distances from NPP sites. The authors of the French study [5] state they only found increases in 2002-2007 but not between 1990-2001, nor over the whole study period, 1990-2007.  But their Table 2 in fact shows an SIR of 1.1 for children <15 and an SIR=1.4 for children below age 5 during 1990-2007 which, due to small numbers, are not statistically significant.

Observed (O) and expected (E) cases of leukaemia in children below age 5 in Germany (16 sites, 1980-2003), Great Britain (13 sites, 1969-2004), Switzerland (4 sites, 1985-2009), and France (19 sites, 1990-2007) are listed in Table 1. Standardised incidence ratios (SIR) are calculated for two distance zones: r<5km and r≥5km. Relative risks (RR) are determined, i.e. the ratios of the SIR within 5km to the SIRs for distances r≥5km. A binomial test is used to investigate whether the relative risks are significantly greater than 1 (one-sided test).

Results

The results for the relative risks in the three data sets are listed in Table 1.
The relative risks are RR=1.45 (p=0.029) in Germany (D), RR=1.39 (p=0.098) in Great Britain (GB), RR=1.46 (p=0.167) in Switzerland (CH), and RR=1.48 (p=0.113) in France (F).
The pooled data from D, GB, CH, F yield RR=1.44 (p=0.0017). 

Discussion

The negative results of the British [3] and Swiss [4] study were used to argue against the findings of the KiKK study [1]. The pooled analysis of the data from Germany, Great Britain, Switzerland, and France, however, yields an even more significant result than the analysis of the German data [2] alone. The resulting relative rsik of 1.44 does not contradict the highly significant relative risk of 2.19 (p<0.001) found in the German KiKK study which used a more sophisticated case control study design. Based on the same data, the German ecological study (2) yields an SIR of 1.41 which is not significant when a two-sided test is used (p=0.066). This illustrates that only large and well designed studies are able to detect leukaemia increases in the immediate vicinity of nuclear power plants.

References

1.  Kaatsch P. Spix C. Schulze-Rath R. Schmiedel S. Blettner M. Leukaemia in young children living in the vicinity of German nuclear power plants. Int J Cancer 2008; 122: 721-726.

2.  Kaatsch P, Spix C, Jung I, Blettner M. Childhood leukaemia in the vicinity of nuclear power plants in Germany. Dtsch Arztebl Int. 2008 Oct;105(42):725-32.

3.  Committee on Medical Aspects of Radiation in the Environment (COMARE). Fourteenth report. Further Consideration of the Incidence of Childhood Leukaemia Around Nuclear Power Plants in Great Britain. London: Health Protection Agency. 2011. http://www.comare.org.uk/press_releases/documents/COMARE14report.pdf

4.  Spycher BD, Feller M, Zwahlen M, Röösli M, von der Weid NX, Hengartner H, Egger M, Kuehni CE. Childhood cancer and nuclear power plants in Switzerland: A census based cohort study. International Journal of Epidemioloy 2011 doi:10.1093/ije/DYR115. http://ije.oxfordjournals.org/content/early/2011/07/11/ije.dyr115.full.pdf+html.

5.  Sermage-Faure C, Laurier D, Goujon-Bellec S, Chartier M, Guyot-Goubin A, Rudant J, Hémon D, Clavel J. Childhood leukaemia around French nuclear power plants - the Geocap study. 2002-2007. Int J Cancer. 2012 Jan 5. doi: 10.1002/ijc.27425. [Epub ahead of print].

Also see my letter to the editor of IJE:

Koerblein A. CANUPIS study strengthens evidence of increased leukaemia rates near nuclear power plants. International Journal of Epidemiology 2012; doi: 10.1093/ije/dyr210 http://ije.oxfordjournals.org/cgi/reprint/dyr210?ijkey=Vi52uOoNNE7T3vs&keytype=ref

Table 1: Relative risks (0-5 km vs. 5+ km zone)