© The Author 2007. Published by Oxford University Press.
CORRESPONDENCE |
Response: Re: Cellular Telephone Use and Cancer Risk: Update of a Nationwide Danish Cohort Study
Affiliations of authors: Institute of Cancer Epidemiology, Copenhagen, Denmark (JS, RJ, JO, CJ); International Epidemiology Institute, Rockville, MD (JB, JM)
Correspondence to: Joachim Schüz, PhD, Institute of Cancer Epidemiology, Department of Biostatistics and Epidemiology, Strandboulevarden 49, Copenhagen, DK-2100, Denmark (e-mail: joachim{at}cancer.dk).
Ahlbom et al. are concerned about our conclusion that our study provides evidence against any large risk of cancer among long-term subscribers of cellular telephones. In support of this concern, Ahlbom et al. reiterate limitations of our study that we noted in our paper and scrutinize our findings for brain tumors and acoustic neuromas.
With respect to brain tumors, Ahlbom et al. appear to imply that a healthy cohort effect could explain the standardized incidence ratio (SIR) of 0.66 for brain tumors more than 10 years after first cellular telephone subscription. We concluded that the healthier lifestyle of cohort members most likely explains the overall decreased cancer rate of men in the cohort and, in particular, the substantial deficits of cancers known to be associated with smoking or alcohol consumption. We have discussed various possible explanations for the decreased brain tumor risk, including a true effect, a healthy cohort effect, and especially chance, noting the lack of a statistically significant dose–response relationship by years since first subscription and the large number of standardized incidence ratios reported in our study. We consider a healthy cohort effect to be extremely unlikely for brain tumors, particularly in view of the absence of any strong association between lifestyle-related factors and brain tumor risk in prior epidemiologic studies of adults (1–3). We advise against encouraging false hopes that a healthy lifestyle is associated with a decreased risk of brain tumors to explain a cellular telephone study finding that lacks a straightforward explanation.
With respect to acoustic neuroma, Ahlbom et al. refer to the Swedish component of an international case–control study (4) that reported increased risks associated with 10 or more years since first cellular telephone use (odds ratio [OR] = 1.9, 95% confidence interval [CI] = 0.9 to 4.1) and with 10 or more years duration of use (OR = 1.6, 95% CI = 0.7 to 3.6); however, in a pooled analysis of data from five countries (5), including Sweden, these odds ratios were attenuated to 1.0 and 1.1, respectively. We judged the pooled analyses to be more appropriate for making inferences on risk than a single finding. As we noted, our acoustic neuroma results are overall consistent with the results of the pooled five-country study (5).
We concluded that our study provides evidence to exclude any large risk of cancer in the observed population at risk. We presented standardized incidence ratios for brain tumor and leukemia specifically for long-term subscribers of 10 or more years in our manuscript. We also evaluated the risk of all cancers according to time since first subscription and found no statistically significant increases in risk for all cancers (SIR = 0.93, 95% confidence interval = 0.87 to 0.98), breast cancer (SIR = 0.92, 95% CI = 0.54 to 1.48), prostate cancer (SIR = 1.10, 95% CI = 0.90 to 1.32), testicular cancer (SIR = 0.77, 95% CI = 0.41 to 1.32), or any other cancer among long-term subscribers. We agree with Ahlbom et al. that the overall evidence regarding cancer risk and short-term use of cellular telephones is reassuring. As stated in the final paragraph of our manuscript, we also agree that further study is warranted to evaluate the possibility of an association between long-term cellular telephone use and brain tumor risk.
REFERENCES
(1) Ohgaki H, Kleihues P. Epidemiology and etiology of gliomas. Acta Neuropathol (Berl) (2005) 109:93–108.[CrossRef][Medline]
(2) Wrensch M, Minn Y, Chew T, Bondy M, Berger MS. Epidemiology of primary brain tumors: current concepts and review of the literature. Neuro-oncol (2002) 4:278–99.[Abstract]
(3) Inskip PD, Linet MS, Heineman EF. Etiology of brain tumors in adults. Epidemiol Rev (1995) 17:382–414.
(4) Lönn S, Ahlbom A, Hall P, Feychting M. Mobile phone use and the risk of acoustic neuroma. Epidemiology (2004) 15:653–9.[CrossRef][ISI][Medline]
(5) Schoemaker MJ, Swerdlow AJ, Ahlbom A, Auvinen A, Blaasaas KG, Cardis E, et al. Mobile phone use and risk of acoustic neuroma: results of the Interphone case-control study in five North European countries. Br J Cancer (2005) 93:842–8.[CrossRef][ISI][Medline]
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J Natl Cancer Inst 2007 99: 655.
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