Re: Mobile phone use and glioma risk: comparison of epidemiological study results with incidence trends in the United States
Little et al compare the “observed” patterns for glioma incidence in the US from 1992-2008 for non-Hispanic whites with estimated rates based on relative risks of glioma reported in the Interphone and Hardell studies. They make a number of arbitrary assumptions to evaluate the potential impact of cellphone use on glioma incidence. Instead of directly using SEER registry incidence figures, they calculate “observed case numbers” using a complex model based on glioma incidence in Los Angeles males aged 60-64 years. They justify their choice because this age group contained the largest and median number of cases. In fact, this age group was not the heaviest users of cellphones a decade earlier, according to surveys of the Pew Foundation.
Little et al over-estimated the numbers of heavy cell phone users in the past. Their findings are consistent with doubled risk for glioma reported in both Interphone and Hardell studies, and in the recent Cardis et al analysis that relies on dosimetry estimates.
Little et al assumed that the baseline population use of cellphones in 1992-96 was <15%. During that period the proportion of these users who used phones heavily was <20% according to Interphone. If the population risk was doubled in heaviest users—as both Interphone Appendix II and Hardell report—then only 3% (20% of 15%) of the total population would have been users in whom a doubled risk of brain cancer might have occurred within a decade.
Contrary to what the authors imply, this study does confirm that predicted glioma rates based on the small proportion of highly exposed people in the Interphone study could be consistent with the observed US data. This confirmatory finding of a 1.5 to 2-fold increased glioma risk with decade long regular use provides evidence of a long-term serious public health issue that must not be ignored.
The last case-control study on cellphone use in the US was produced in 2001. Given the tremendous growth and changes in use of the technology, and concerns that it may also be linked with reproductive and neurodegenerative impacts, it is critical that additional studies be carried out focusing on those who have begun using cellphones earlier and more heavily in life.
Competing interests: No competing interests