Letter to the Editor

Reader’s Response: Meningioma and mobile phone use—a collaborativecase–control study in five North European countriesFrom L LLOYD MORGAN

There are many problems in this recently publishedInterphone study by Lahkola et al.1 Among them areunexplained differences in the number of controlsand cases, a gender mismatch among controls, astated concern for the ‘implausibly high reportedmean daily hours of use’, and a large fraction ofodds ratios (ORs) <1.

Control and case differencesThe authors report, ‘. . . the slightly smaller numbersof cases [1] than in national reports are due to reviseddiagnosis, date of diagnosis or history of previousbrain tumour’. This would imply that errata shouldhave been sent to the journals that published thesethree national studies.2–4 What is not reported is thata considerably larger number of controls (55 total, 47from the Swedish study) reported in the nationalreports are missing in this study. Also, this is thethird five-country study. The total number of reportedcontrols in this study was 3299, in the five-countryglioma study the reported number of controls was3301,5 and in the five-country acoustic neuromastudy the reported number of controls was 2661.6

These differences in the number of controls is partic-ularly hard to understand because the paper states:‘Frequency-matching employed throughout theInterphone study allowed us to utilize the entire con-trol group recruited for all intracranial tumours(glioma, meningioma and acoustic neuroma) in thematched strata of the meningioma cases, to increasestatistical power’. Finally, it is not clear when the13-country pooled Interphone data results are finallypublished if the data from this paper or the data fromthe three previously published national studies will beused. This should be clarified.

Gender mismatch among controlsThe female/male ratio for cases was 3.02 and for con-trols was 1.16. The authors cite the known factthat incidence of meningioma is higher amongwomen than men. In the USA, the female/male

ratio is 2.27.7 The ratio difference between the USAand these five countries suggests there may be anincreased risk of meningioma from cellphone use inwomen relative to men but because no gender riskdata is reported this cannot be known.

Besides the likely introduction of gender biasthroughout the analysis, the use of cut points basedon control use creates a serious problem. Twice thepaper reports using controls to determine cut-points:‘An additional analysis of the subgroup with the high-est cumulative number of calls and cumulative hoursof use was performed with the cut-point defined asthe value among the 10% of controls with the heavi-est mobile phone use (among regular users)’, and ‘Inanalyses of categorical exposure variables, the cut-points were chosen based on the distribution amongcontrols’.1 Given this is a paper about the possibilityof a risk of meningioma from cellphone use, it is hardto understand why controls would be used to deter-mine cut-points particularly when the gender ratio ofcontrols are so very different from cases for a diseasewith a known increased incidence in women.

Concern for implausibly highreported mean daily hours of useThe paper reports a significantly increased risk ofmeningioma per 100 h of cellphone use [OR¼ 1.005,95% confidence interval (CI) 1.001–1.010], yetexpresses concern because ‘. . . this was driven by asmall number of very high values which in turnreflected subjects with implausibly high reportedmean daily hours of use (2.4 hours per day and 3.5hours a day for controls and cases)’.1 There is noexplanation why this would be implausible. Whilethis use per day seems quite plausible to me, myviews, similar to the authors of this paper, are irrele-vant. To verify if this is plausible or not, cellphoneproviders could have been queried for aggregatehours per day of use by percentile of all subscribers.

Large fraction of ORs <1Overall, there were 72 reported ORs, eitherin tables or in the text, 64 of these were <1, 29 ofthese 64 were significantly <1. The authors note this

Central Brain Tumor Registry of the United States, Hinsdale, IL,USA. E-mail: bilovsky@aol.com

Published by Oxford University Press on behalf of the International Epidemiological Association [2009]

all rights reserved.

International Journal of Epidemiology 2009;1–2

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Int. J. Epidemiol. Advance Access published April 22, 2009

when they obliquely state: ‘. . . mobile phone use wasassociated with an apparently reduced risk of menin-gioma’. Stated more directly, they were reportingresults that show use of a cellphone protects theuser from risk of a meningioma with P-values aslow as 0.000022 (OR¼ 0.68, 95% CI 0.57–0.85 for<125 h of cumulative use). Similar incredulous find-ings have been seen in all 14 of the Interphone braintumour studies published to date. The authors shouldbe congratulated, as they are the first to directly com-ment on these findings of protection. All previouspapers have only reported the OR and CIs in the con-text of finding ‘no risk’.

Conflict of interest: All statements are mine andmine alone and do not represent positions or opinionsof the Central Brain Tumor Registry of the UnitedStates.

References1 Lahkola A, Salminen T, Raitanen J et al. Meningioma and

mobile phone use—a collaborative case-control study in

five North European countries. Int J Epidemiol 2008;37:1304–13.

2 Lonn S, Ahlbom A, Hall P et al. Long-term mobile phoneuse and brain tumor risk. Am J Epidemiol 2005;161:526–35.

3 Collatz Christensen H, Schuz J, Kosteljanetz M et al.Cellular telephones and risk for brain tumors, a popula-tion-based, incident case-control study. Neurology 2005;64:1189–95.

4 Klaeboe L, Blaasaas KG, Tynes T. Use of mobile phones inNorway and risk of intracranial tumours. Eur J CancerPrev 2007;16:158–64.

5 Schoemaker MJ, Swerdlow AJ, Ahlbom A et al. Mobilephone use and risk of acoustic neuroma: results of theInterphone case–control study in five North Europeancountries. Br J Cancer 2005;93(7):842–48.

6 Lahkola A, Auvinen A, Raitanen J et al. Mobile phoneuse and risk of glioma in 5 North European countries.Int J Cancer 2007;120:1769–75.

7 CBTRUS. Statistical Report: Primary Brain Tumors in theUnited States, 2000–2004. Hinsdale, IL, USA: CentralBrain Tumor Registry of the United States, 2008.

doi:10.1093/ije/dyp197

2 INTERNATIONAL JOURNAL OF EPIDEMIOLOGY