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Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case-control study

BMJ 2005; 330 doi: https://doi.org/10.1136/bmj.330.7503.1290 (Published 02 June 2005) Cite this as: BMJ 2005;330:1290

Re: Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case- control study.

Re: Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case- control study.

Leeka Kheifets1, Maria Feychting2, Joachim Schüz3

1. Department of Epidemiology, School of Public Health, UCLA, CA, USA

2. Institute of Environmental Medicine, Karolinska Institutet, Sweden

3. Institute of Cancer Epidemiology, Danish Cancer Society, Denmark

We have read with interest the paper from Draper and colleagues [1]. Given its large size the risk estimates in the paper should be stable. Furthermore, because contact with the subject was not necessary selection bias due to the differential participation among cases and controls, which plagued some of the previous studies [2], has been avoided. Thus we were particularly surprised by the dependence of the results on the chosen control group noted by the authors, (who used CNS and other cancer controls for leukaemia cases in one of the comparisons). To explore this further we combined all controls into one group and used it for comparison. We felt this is justified based on both theoretical and empirical grounds: exposure at birth among controls chosen for leukaemia, brain tumours and other cancers should not depend on the cancer subtype; crude odds ratios calculated by us did not differ (beyond first decimal) from the matched results presented by authors (data not shown).

Use of the combined control group revealed a pattern different than the one presented in the original paper (Table 1). As would be expected, results for all cancers combined show no relation to the distance. For both leukaemia and brain cancer results at two distances are noteworthy: for the 50-100 meters category an excess of leukaemia and a deficit for brain tumours is observed. For the 500-600 meters category we observed a modest excess for both leukaemia and brain tumours. Of note is that the trend reported in the original paper is not present when the combined control group is used, thus indicating that the trend depended on the leukaemia controls rather than on the leukaemia cases. We agree with the authors that the results of this study do not support a possible magnetic field association, as has been reported by the IARC monograph [2]. However, distance is known to be a very poor predictor of magnetic field exposure, and therefore, results of this material based on calculated magnetic fields, when completed, should be much more informative.

Further insight might be gained by details on the methods used for the control selection and sensitivity analyses by age, sex and time period.

1. Draper G, Vincent T, Kroll ME, Swanson J. Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case- control study. BMJ 2005; 330:1290-2.

2. Ahlbom A, Day N, Feychting M, et al. A pooled analysis of magnetic fields and childhood leukaemia. Br J Cancer, 83, 692-8 (2000).

3. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Vol 80 Non Ionizing radiation, Part 1: Static and Extremely Low – Frequency Electric and Magnetic Fields. 2002

Distance of address at birth from nearest National Grid line and estimated odds ratios using all controls combined

Leukemia CNS Other tumours All cancer combined All controls
Distance No. cases OR (95% CI) No. cases OR (95% CI) No. cases OR (95% CI) No. cases OR (95% CI) No. controls
0-49 5 0.94 (0.34-2.57) 3 0.83 (0.24-2.84) 7 1.00 (0.41-2.42) 15 0.94 (0.46-1.90) 16
50-99 19 1.73 (0.99-3.05) 4 0.53 (0.19-1.51) 15 1.04 (0.56-1.91) 38 1.15 (0.72-1.84) 33
100-199 40 1.18 (0.82-1.70) 26 1.12 (0.73-1.73) 37 0.83 (0.57-1.20) 103 1.01 (0.77-1.33) 102
200-299 44 0.93 (0.66-1.30) 38 1.17 (0.82-1.68) 66 1.05 (0.78-1.41) 148 1.04 (0.82-1.31) 143
300-399 61 1.23 (0.91-1.66) 35 1.04 (0.72-1.50) 79 1.21 (0.92-1.59) 175 1.18 (0.95-1.47) 149
400-499 78 1.15 (0.89-1.50) 40 0.86 (0.62-1.22) 80 0.89 (0.69-1.16) 198 0.97 (0.80-1.18) 204
500-599 75 1.24 (0.95-1.63) 54 1.31 (0.96-1.78) 86 1.08 (0.83-1.39) 215 1.18 (0.97-1.44) 182
™600 9378 1 (ref) 6405 1 (ref) 12406 1 (ref) 28189 1 (ref) 28252

Competing interests:
For LK work for EPRI and consulting with utilities

Competing interests: No competing interests

22 June 2005
Leeka Kheifets
Professor
Maria Feychting , Joachim Schuz
UCLA, Los Angeles, 90095