animals (Scientific Committee on Emerging and Newly Identified Health Risks 2009). The major biases and uncertainties in interpretation of the Interphone study are similar to those in other interview-based case–control studies of brain tumors and mobile phones. The exceptional size of the Interphone study has not proved to be a criti- cal strength—issues of bias and misclassifica- tion have proved far more important than tightness of CIs. Therefore, more studies of the same basic design as Interphone, based on recall of phone use, no matter how care- fully designed and conducted, are unlikely to add materially to our knowledge. There are other epidemiologic designs that do not share these weaknesses (although they have others), whose results need consideration in relation to the uncertainties remaining after Interphone: studies of the effects of occupational and resi- dential RF exposures, record linkage-based case–control and cohort studies of phone use, and trend analyses of brain tumor incidence rates in the general population. The occupational studies, and those of cancer risk in relation to residential proximity to RF broadcasting towers, have not indi- cated any cancer risk, although they have been methodologically weak (Ahlbom et al. 2004). Studies that have linked private non- corporate telephone subscription records to cancer registry records (in certain Nordic countries) (Auvinen et al. 2002; Schüz et al. 2006) or death records (in the United States) (Dreyer et al. 1999) have the strengths that they avoid recall bias and misclassification and avoid participation bias. They have the weaknesses, however, not present in inter- view case–control studies such as Interphone, that the subscription data exclude corporate subscriptions, which in the early years were likely often to have been held by heavy users, and that the named subscriber is not nec- essarily the user. These problems are likely to have diluted any true association. A U.S. cohort study (Dreyer et al. 1999) was halted 1 year after recruitment and so was essen- tially uninformative. A national records-based case–control study in Finland (Auvinen et al. 2002) based on very short durations of use found a borderline significantly raised risk of glioma in ever-users, with some evidence for a relation to analog not digital phone use. A Danish cohort study (Schüz et al. 2006) followed 420,000 phone subscribers over a period of 7–21 years and gave no indication of raised risk of glioma or meningioma or any trend in risk with duration since first use. Trend data. Analyses of secular trends in brain tumor incidence, in countries that have had good-quality diagnostic facilities and can- cer registration, can give powerful evidence constraining what can reasonably be proposed as an etiologic relationship. The dramatic rise in mobile phone use over a relatively short period of time provides an unusual opportu- nity to assess the potential for a causal effect on cancer occurrence through high-quality, unbiased descriptive epidemiologic data. Because substantial misclassification is inevi- table in recall-based exposure information from the Interphone interviews, it follows that if the raised relative risk observed in the top decile of users in the Interphone study were caused by phone use, not by chance or artifact, then the true effect would likely be much larger and therefore more easily detect- able in population cancer incidence trends. However, data from the Nordic countries for 1974–2003 (Deltour et al. 2009) and chil- dren in the Nordic countries for 1985–2006 (Schmidt et al. 2011) and from Switzerland for 1969–2002 (Roosli et al. 2007), England for 1998–2007 (de Vocht et al. 2011), and the United States for 1992–2006 (Inskip et al. 2010) and for 1987–2007 (Kohler et al. 2011) showed no indication of increases in brain tumor incidence in relation to the intro- duction and growing use of mobile phones, up to 20 years after their introduction and 10 years after their use became widespread. This does not appear compatible with the greatest risk shown in the Interphone study—the ORs of about 4 within 5 years of first use for individuals using a phone for ≥1,640 hr cumulatively—or with the risk esti- mates using a “low user” baseline group, given in the appendix of the Interphone report (Interphone Study Group 2010). The Interphone levels of exposure were those in the population in 2003 and ear- lier; since then, prevalence and probably levels of use have increased greatly. Future examination of cancer incidence trend data over the next few years, especially by age of occurrence and anatomic location of tumors, should greatly clarify whether mobile phones cause brain tumors: If there are no apparent effects on trends in the next few years, after almost universal exposure to mobile phones in Western countries, it will become increas- ingly implausible that there is a material causal effect. Conversely, if there are unexplained rising trends, this will not in itself prove cau- sation, but will give a case to be answered. Supplemental Material, Figure 1 (http:// dx.doi.org/10.1289/ehp.1103693), shows the most recently available data, up to 2009, from Sweden, one of the earliest adopters of mobile phones (see Supplemental Material, Figure 2); the data give evidence against an impact of mobile phone use on brain tumor occurrence. Conclusions Interphone is an impressively large study with multiple indices of exposure. However, it has some methodological deficits, largely inevitable in recall-based case–control studies, Environmental Health Perspectives • volume 119 | number 11 | November 2011 Mobile phones and brain tumor risk which limit interpretation of its findings. Such evidence as it provides, combined with the results of biological and animal studies, other epidemiologic studies, and brain tumor incidence trends, suggest that within the first 10–15 years after first mobile phone use there is unlikely to be a material increase in risk of adult brain tumors resulting from mobile phone use. At present there are no data on risk of childhood tumors. The deficiencies of exposure measurement, because of recall misclassification in studies such as Interphone, and because of misidenti- fication of users in records-based studies such as the published cohorts, leave it doubtful that either study type could reliably detect a small effect, if one existed. Both for this reason and because research cannot in principle prove the complete absence of an effect but only place limits on its possible magnitude, there is bound to remain some uncertainty for many years to come. The limited duration of data yet available, which is mainly for up to 10 years of exposure and to a lesser extent for a few years beyond this, also leave uncertainty because of the potential for long lag period effects, especially for meningioma, which is generally slower growing than glioma. The possibility of a small or a longer-term effect thus cannot be ruled out. 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