Mobile phone use and glioma risk: comparison of epidemiological study results with incidence trends in the United States

Abstract

Objective: In view of mobile phone exposure being classified as a possible human carcinogen by the International Agency for Research on Cancer (IARC), we determined the compatibility of two recent reports of glioma risk (forming the basis of the IARC's classification) with observed incidence trends in the United States.

Design: Comparison of observed rates with projected rates of glioma incidence for 1997-2008. We estimated projected rates by combining relative risks reported in the 2010 Interphone study and a 2011 Swedish study by Hardell and colleagues with rates adjusted for age, registry, and sex; data for mobile phone use; and various latency periods.

Setting: US population based data for glioma incidence in 1992-2008, from 12 registries in the Surveillance, Epidemiology, and End Results (SEER) programme (Atlanta, Detroit, Los Angeles, San Francisco, San Jose-Monterey, Seattle, rural Georgia, Connecticut, Hawaii, Iowa, New Mexico, and Utah).

Participants: Data for 24,813 non-Hispanic white people diagnosed with glioma at age 18 years or older.

Results: Age specific incidence rates of glioma remained generally constant in 1992-2008 (-0.02% change per year, 95% confidence interval -0.28% to 0.25%), a period coinciding with a substantial increase in mobile phone use from close to 0% to almost 100% of the US population. If phone use was associated with glioma risk, we expected glioma incidence rates to be higher than those observed, even with a latency period of 10 years and low relative risks (1.5). Based on relative risks of glioma by tumour latency and cumulative hours of phone use in the Swedish study, predicted rates should have been at least 40% higher than observed rates in 2008. However, predicted glioma rates based on the small proportion of highly exposed people in the Interphone study could be consistent with the observed data. Results remained valid if we used either non-regular users or low users of mobile phones as the baseline category, and if we constrained relative risks to be more than 1.

Conclusions: Raised risks of glioma with mobile phone use, as reported by one (Swedish) study forming the basis of the IARC's re-evaluation of mobile phone exposure, are not consistent with observed incidence trends in US population data, although the US data could be consistent with the modest excess risks in the Interphone study.

Fig 1 Mobile phone subscriptions per capita in the US, by year

Fig 2 Observed and projected rates (95% CI) of malignant glioma in non-Hispanic white people, by latency period and various assumed levels of relative risk associated with ever using a phone

Fig 3 Observed and projected rates (95% CI) of malignant glioma in non-Hispanic white people, by histological type and WHO grade of glioma, using the relative risks, periods of latency, and cumulative hours of phone use from the Swedish study and Interphone study

Fig 4 Observed and projected rates (95% CI) of malignant glioma in non-Hispanic white people, by tumour location, using the relative risks, periods of latency, and cumulative hours of phone use from the Swedish study and Interphone study