Re: Mobile phone use and glioma risk: comparison of epidemiological study results with incidence trends in the United States
Re: Mobile phone use and glioma risk: comparison of epidemiological study results with incidence trends in the United States. BMJ 2012;344:e1147
Little et al studied the incidence rates of glioma during 1992-2008 in the United States and compared with odds ratios for glioma associated with mobile phone use in the 2010 Interphone publication1 and our pooled results published in 2011.2 However, an important methodological issue that was not stated in the abstract or in Figures 2-4, but can be found in the web appendix, is that observed rates were based on men aged 60-64 years from the Los Angeles SEER registry as the baseline category. These data were used to estimate rates in the entire dataset, men and women aged > 18 years and all 12 SEER registries. Thereby numerous assumptions were made as pointed out by Kundi and Davis et al. (Rapid Response 17 March 2012).
Our patients with brain tumour were diagnosed during 1997-2003. Using only men, as Little et al did, ignores the fact that women had less frequent use of mobile phones than men, see Table 1. Overall 31 % of women reported such use versus 57 % of men. Furthermore, use varies with age group with a large difference according to age, as we have explored in our publications.2,3 Thus, the age group 60-64 year old men is not valid to use for these calculations.
Little et al do not explain how they obtain different results on incidence trends based on the Hardell group studies and Interphone. They ignore that we assessed also use of cordless desktop phones in contrast to Interphone. As pointed out by IARC the appropriate exposure category for wireless phone emissions is both mobile and cordless phones.4 We have compared our results with Interphone considering different age groups and exposure categories in these publications. Thereby the results are similar for both study groups.5 We have now updated the results based on our 2011 publication,2 Table 2. We restricted cases and controls to the age group 30-59 years and disregarded use of cordless phones as in Interphone. Odds ratios are in fact somewhat lower in our study that in Interphone. It is thus remarkable that the projected incidence rates by Little et al are so different based on our results compared with Interphone although odds ratios are similar. It should be added that Little et al present wrong latency periods for the results in our studies both in the publication and in the web appendix.
There are several other points that may be added. The results for oligodendroglioma > 10 year latency in our study are wrong in the web appendix, should be OR 2.2, 95 % CI 0.9-5.4 and not OR 1.4, 95 % CI 0.9-2.3. Another example is that the results for anatomical localisations and tumour grade [in Table 5] by Little et al are based on numerous assumptions from SEER data, Interphone and the Hardell group studies. They seem not to have paid attention to the fact that the fraction of mobile phone users differs for gender and age groups, see our Table 1. Furthermore, only we have published results for both low-grade and high-grade astrocytoma,6 results that are ignored by Little et al. We have now analysed the data further using our 2011 publication,2 see Table 3. Obviously the risk is higher for high-grade than low-grade astrocytoma for latency >10 years. This is of interest considering the statistically significant yearly increasing incidence of high-grade glioma in the SEER data for 1992-2008, +0.64%, 95% CI 0.33 to 0.95.
In summary the conclusion by Little et al that “Raised risk of glioma with mobile phone use, as reported by one (Swedish) study....are not consistent with observed incidence trends in the US population data...” goes far beyond scientific evidence and what would be possible to show with the faulty methods used in the study. We agree with Kundi that there is much room for improvement of the BMJ review process, as we have exemplified7 regarding another recent BMJ publication.8
1. INTERPHONE Study Group. Brain tumour risk in relation to mobile telephone use: results of the INTERPHONE international case-control study. Int J Epidemiol 2010;39(3):675-694.
2. Hardell L, Carlberg M, Hansson Mild K. Pooled analysis of case-control studies on malignant brain tumours and the use of mobile and cordless phones including living and deceased subjects. Int J Oncol 2011;38(5):1465-74.
3. Hardell L, Carlberg M. Mobile phones, cordless phones and the risk for brain tumours. Int J Oncol 2009;35(1):5-17.
4. Baan R, Grosse Y, Lauby-Secretan B, El Ghissassi F, Bouvard V, Benbrahim-Tallaa L, et al. Carcinogenicity of radiofrequency electromagnetic
fields. Lancet Oncol 2011;12(7):624-6.
5. Hardell L, Carlberg M, Hansson Mild K. Re-analysis of risk for glioma in relation to mobile telephone use: comparison with the results of the Interphone international case-control study. Int J Epidemiol 2011;40(4):1126-8.
6. Hardell L, Carlberg M, Hansson Mild K. Pooled analysis of two case-control studies on use of cellular and cordless telephones and the risk for malignant brain tumours diagnosed in 1997-2003. Int Arch Occup Environ Health 2006;79(8):630-9.
7. Soderqvist F, Carlberg M, Hardell L. Review of four publications of the Danish cohort study on mobile phone subscribers and risk of brain tumors. Rev Environ Health 2012, In press.
8. Frei P, Poulsen AH, Johansen C, Olsen JH, Steding-Jessen M, Schüz J. Use of mobile phones and risk of brain tumours: update of Danish cohort study. BMJ 2011;343:d6387.doi: 10.1136/bmj.d6387
Competing interests: No competing interests