The glioma incidence trends in the USA in 1992-2008 were compared with results of the two epidemiological studies (Interphone Study Group (2010), and a Swedish group (Hardell et al (2011)) forming the basis of the IARC Working Group classification of radiofrequency electromagnetic fields (Baan et al (2011)) .
Projected rates were estimated by combining relative risks reported by the two studies with rates adjusted for age, registry and sex; data for mobile phone use (cumulative call time; cumulative number of calls); and various latency periods (time since start of regular use).
|Reference group 1||no mobile phone use|
|Group 2||mobile phone use|
|Reference group 3||time since start of regular use: 1-1.9 years|
|Group 4||time since start of regular use: 2-4 years|
|Group 5||time since start of regular use: 5-9 years|
|Group 6||time since start of regular use ≥ 10 years|
|Reference group 7||cumulative call time: < 5 h|
|Group 8||cumulative call time: 5.0-12.9 h|
|Group 9||cumulative call time: 13-30.9 h|
|Group 10||cumulative call time: 31-60.9 h|
|Group 11||cumulative call time: 61-114.9 h|
|Group 12||cumulative call time: 115-199.9 h|
|Group 13||cumulative call time: 200-359.9 h|
|Group 14||cumulative call time: 360-734.9 h|
|Group 15||cumulative call time: 735-1639.9 h|
|Group 16||cumulative call time: ≥ 1640 h|
|Reference group 17||cumulative number of calls: < 150|
|Group 18||cumulative number of calls: 150-349|
|Group 19||cumulative number of calls: 350-749|
|Group 20||cumulative number of calls: 750-1399|
|Group 21||cumulative number of calls: 1400-2549|
|Group 22||cumulative number of calls: 2550-4149|
|Group 23||cumulative number of calls: 4250-6799|
|Group 24||cumulative number of calls: 6800-12799|
|Group 25||cumulative number of calls: 12800-26999|
|Group 26||cumulative number of calls: ≥ 27000|
Age-specific incidence rates of glioma remained generally constant in 1992-2008, a period coinciding with a substantial increase in mobile phone use from close to 0 % to almost 100 % of the population of the USA. If mobile phone use is associated with glioma risk the authors expected glioma incidence rates to be higher than those observed, even with a long latency period of 10 years and a low relative risk of 1.5.
Based on relative risks of glioma by tumor latency and cumulative hours of mobile 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 either non-regular users or low users of mobile phones were taken as reference group, and if relative risks were constrained to be more than 1.
The authors concluded that raised risks of glioma with mobile phone use as reported by one Swedish study are not consistent with observed glioma incidence trends in USA population data. However, the USA data could be consistent with the modest excess risks in the Interphone study.