The Cohort Study on Mobile Phones and Health (COSMOS)

The letter discusses serious problems with a recent COSMOS paper that provided interim results about brain tumor risk from mobile phone use. The letter calls for a retraction of the paper’s conclusions and demands that the data set be made available to independent investigators who have no industry ties. Excerpts from the letter appear below.

We write to point out serious methodological problems with the Cohort Study on Mobile Phones and Health (COSMOS) brain tumor risk paper (Feychting et al., 2024). Because of these flaws, the study does not provide reliable estimates of the risks of tumors associated with exposure to mobile phone radio frequency radiation (RFR). This paper which summarizes interim results from this 25-plus year cohort study (Schüz et al., 2011) demonstrates many of the overall study’s shortcomings….

1. Problems with exposure assessment

… Misclassification of RFR exposure was substantial because the amount of exposure from a mobile phone varies by up to four orders of magnitude depending on the cellular network technology and the strength of the signal from the cell tower (Wall et al., 2019). COSMOS did not account for this variability. The study also did not control for other sources of RFR exposure, including cordless phones, personal wireless devices, Wi-Fi routers, and cell towers….

Since almost everyone in this cohort study regularly used mobile phones at baseline (including two-thirds who used mobile phones for 10 or more years) and many were exposed to others sources of RFR (e.g., cordless DECT phones, cell towers, Wi-Fi), there was no unexposed group. That the authors chose to use the bottom 50 % of the mobile phone use distribution as the reference group instead of a more extreme percentile cutoff (e.g., the bottom decile of mobile phone use) does not seem defensible….

2. Problems with outcome assessment

The incidence of brain tumors may be under-reported in the five national cancer registries that this study relied upon to assess outcomes….

3. Latency, type and location of tumors

Most human cancers have long latencies, requiring many years to decades after exposure to carcinogens before clinical presentation and diagnosis (Armenian, 1987, Nadler and Zurbenko, 2022). Accordingly, it is critical in cohort studies like COSMOS to stratify on the total length of time between initiation of any given level of exposure – in this case to RFR – and the date of cancer diagnosis, especially since so many members of the COSMOS cohort already had many years of substantial RFR exposure when recruited….

This interim study by Feychting et al. (2024) does not have a sufficient number of subjects followed for more than a decade after RFR exposure began to rule out elevated risks of these two tumors after the most relevant latent periods for carcinogenesis….

4. Statistical issues

Although the authors acknowledged that “Statistical power was limited for meningioma and acoustic neuroma,” we contend that glioma with only 149 incident cases in this study of 1.836 million person years also had limited statistical power. The confidence intervals for the hazard ratios were large. Moreover, the power analysis in the COSMOS design paper (Table 2, Schüz et al., 2011) assumed an annual incidence rate of 15 per 100,000 for brain tumors, whereas the glioma annual incidence rate in the current study was 8.11 per 100,000. Thus, no analysis of tumor risk in this paper had adequate statistical power.

We question whether the study adequately addressed the heterogeneity among countries….

The Data Availability section of the paper states, “The data that has been used is confidential.” If the authors are using this as the reason not to share their data, then the results cannot be confirmed by independent investigators. Since these data have potentially important policy implications, the data set must be accessible to other researchers….

5. Industry research funding

Funding bias is well-recognized in biomedical research (Bekelman et al., 2003). Industry-funded studies were less likely to report statistically significant health-related effects associated with mobile phone use than non-industry funded studies (Huss et al., 2007, Moskowitz et al., 2020). For example, a review of experimental studies concluded, “industry-sponsored studies were least likely to report results suggesting effects… The source of funding and conflicts of interest are important to consider in this area of research (van Nierop et al., 2010).

COSMOS was partially funded by the telecommunications industry in three countries, Finland, Sweden, and the United Kingdom (Feychting et al., 2024)….

6. Conclusions

Given the serious methodologic problems with this interim COSMOS paper discussed above, we recommend that the authors retract their conclusion: “Our findings to date, together with other available scientific evidence, suggest that mobile phone use is not associated with increased risk of developing these tumours.”.

To support this assertion the authors relied on evidence from three cohort studies (Feychting et al., 2024, Schüz et al., 2006, Schüz, 2022) with weak methodology (Ahlbom et al., 2007, Birnbaum et al., 2022, Moskowitz, 2022, Söderqvist et al., 2012). For example, IARC concluded, “reliance on subscription to a mobile phone provider, as a surrogate for mobile phone use, could have resulted in considerable misclassification in exposure assessment” (Baan et al., 2011). Schüz et al. (2022) did not provide data on cumulative phone use. To support their “no association” conclusion, the COSMOS authors also cited time-trend studies; yet, these studies reported significant increases in brain tumor incidence in age-specific subgroups (e.g., de Vocht, 2021, Deltour et al., 2022, Elwood et al., 2022: Ostrom et al., 2022). Finally, the COSMOS authors cited a review of case-control studies that dismissed the results of the cumulative call time analysis by relegating it to the appendix (i.e., Supplemental Figure 2, Röösli et al., 2019).

In contrast to Röösli et al., 2019, Choi et al., 2020 systematic review and meta-analysis of 46 case-control studies”found significant evidence linking cellular phone use to increased tumor risk, especially among cell phone users with cumulative cell phone use of 1000 or more hours in their lifetime,” and called for high quality, prospective cohort studies to confirm the results of the case-control research.

The COSMOS paper on brain tumor risk:

Background  Each new generation of mobile phone technology has triggered discussions about potential carcinogenicity from exposure to radiofrequency electromagnetic fields (RF-EMF). Available evidence has been insufficient to conclude about long-term and heavy mobile phone use, limited by differential recall and selection bias, or crude exposure assessment. The Cohort Study on Mobile Phones and Health (COSMOS) was specifically designed to overcome these shortcomings.

Methods  We recruited participants in Denmark, Finland, the Netherlands, Sweden, and the UK 2007–2012. The baseline questionnaire assessed lifetime history of mobile phone use. Participants were followed through population-based cancer registers to identify glioma, meningioma, and acoustic neuroma cases during follow-up. Non-differential exposure misclassification was reduced by adjusting estimates of mobile phone call-time through regression calibration methods based on self-reported data and objective operator-recorded information at baseline. Hazard ratios (HR) and 95% confidence intervals (CI) for glioma, meningioma, and acoustic neuroma in relation to lifetime history of mobile phone use were estimated with Cox regression models with attained age as the underlying time-scale, adjusted for country, sex, educational level, and marital status.

Results  264,574 participants accrued 1,836,479 person-years. During a median follow-up of 7.12 years, 149 glioma, 89 meningioma, and 29 incident cases of acoustic neuroma were diagnosed. The adjusted HR per 100 regression-calibrated cumulative hours of mobile phone call-time was 1.00 (95 % CI 0.98–1.02) for glioma, 1.01 (95 % CI 0.96–1.06) for meningioma, and 1.02 (95 % CI 0.99–1.06) for acoustic neuroma. For glioma, the HR for ≥ 1908 regression-calibrated cumulative hours (90th percentile cut-point) was 1.07 (95 % CI 0.62–1.86). Over 15 years of mobile phone use was not associated with an increased tumour risk; for glioma the HR was 0.97 (95 % CI 0.62–1.52).

Conclusions  Our findings suggest that the cumulative amount of mobile phone use is not associated with the risk of developing glioma, meningioma, or acoustic neuroma.

References (in chronological order; all papers are open access)