Comments on de Vocht et al. “time trends (1998–2007) in brain cancer incidence rates in relation to mobile phone use in England”

Many, including the authors of the article on time trends of brain tumor incidence in England, have expressed the belief that ‘‘given thewidespread use and nearly two decades elapsing since mobile phones were introduced, an association should have produced a noticeable increase in the incidence of brain cancer by now’’ [de Vocht et al., 2011]. However, this belief is unfounded. In a recent article I have shown that given the pattern of mobile phone use, any conceivable effect on brain tumor risk must remain, for the time being, within random fluctuation of incidences in populations the size of England [Kundi, 2010]. Depending on the time trends ofmobile phone use, an increasemay be seen in only a few years or in a decade. The reason that the incidence of brain tumors lag behind the increase inmobile phone use is twofold: first, brain tumors have long latencies with averages between 20 and 40 years; second, an influence only on tumor development and not on tumor initiation can be observed for short exposure durations. The latter has important consequences on the increase in incidences that can possibly occur. I have already mentioned in 2004 that the incidence increase is limited by the slope of the age-incidence function [Kundi, 2004]. For all brain tumors, this slope is shallow (and for some even negative). Assuming a reasonable yet very strong increase in the tumor growth rate of 50%, the incidence cannot be significantly increased during the period of observation of de Vocht et al. According to the Organisation for Economic Cooperation and Development (OECD) data, mobile phone subscription rates in the United Kingdom (UK) were 1.9% in 1990, rose to 9.8% in 1995, and reached 100% in 2004. Since these subscription rates are relative to the total UK population, relating them to the adult population of 20–69 years that were the predominant users at that time will give rates about 1.5 times higher. As of 2007, the proportion of the UK population within this age range using a mobile phone for 10 or more years is estimated as 21.5%; 52% are estimated with 5–9 years of use, and the remaining 26.5%with less than 5 years of use. These figures are in good agreement with usage data in controls of the UK branch of the Interphone study [Hepworth et al., 2006]. Considering that the area of the brain receiving the highest exposure during mobile phone use is the temporal lobe, malignant brain tumors in this area are of particular interest. In England, the age-log-incidence function of malignant temporal lobe brain tumors (International Classification of Diseases (ICD) 10: C71.2) has a slope of 0.06 natural log units per year of age within the age range of 20–69 years, corresponding to an approximate 80% increase per 10 years of age [UK Office for National Statistics, 2011]. Assuming an increase in the tumor growth rate from mobile phone use of 50%, the age-log-incidence function is shifted by 50% of the duration of mobile phone use. Hence, the relative incidence increase from 10 years of mobile phone use under these assumptions amounts to 1.35, and from 5 years use to 1.16. Furthermore, for an effect on growth rate to occur the mobile phone must be used on the same side as the tumor is growing. As a conservative estimate we assume that actual ipsilateral exposure occurs in half of the mobile phone users. Let the incidence at age A be exp(bþ gA), with g the slope (0.06) of the age-logincidence function and b its intercept, then the incidence in a fraction ps with s years of ipsilateral mobile phone use is exp(bþ g(Aþ s 0.5)). It follows that the overall incidence at this age is given by: