In this meta-analysis, we found no association between mobile/cellular phone use and risk of glioma and acoustic neuroma no matter in main or subgroup analyses. For meningioma, decreased risk was observed mobile phone use was associated , especially when the time since first use was less than 10 years, while the protective effect disappeared in longer term (more than 10/11 years).
As for glioma, our result showed no association correlation between mobile phone use of any duration and glioma risk when pooled data of time since first use from 6 articles into meta-analysis, which was consistent with the previous study [26-29]. However, several research showed long-term mobile phone use may be associated with an increased risk of glioma: Yang, M., et al. (2017) reported the significant positive association between long-term mobile phone use (minimum, 10 years) and glioma (OR = 1.44; 95% CI = 1.08–1.91) [29], Y. Wang (2016), also found an association between mobile phone use more than 5 years and glioma risk (OR = 1.35; 95% CI=1.09–1.62; I²=91.9%; P < 0.05) [28], and Prasad, M. found that for
mobile phone use of 10 years or longer (or >1640 h), the overall result of the meta-analysis showed a 1.33 times increase in risk [27]. Nevertheless, the INTERPHONE Study Group found no significant association between long-term mobile use and the risk of glioma (OR, 1.49; 95% CI, 0.80 -2.78; I²= 91.5%) [9]. But their result showed significant heterogeneity, so whether the result was credible enough should be considered. Study quality and source of funding could also influence the research outcomes [27]. Thus, larger and longer studies are required to better characterize this possible link: the dose-response relationship exist between mobile/cellular phone use. It is known that there are biological differences between low-grade glioma and high grade-glioma. Low-grade glioma, with a long latency period, is potentially more vulnerable to radiation from mobile phones, While high-grade disease has a short latency period [29]. As the knowledge of key molecular alterations that provided superior prognostication related to glioma developed fast [30], the linkage between mobile phone usage and glioma risk should be further investigated and discussed.
Our results also showed that regular use of mobile phones is associated with the risk of meningioma (OR: 0.84, 95%CI: 0.78-0.91, I²=47.3%, p=0.091). When the subgroup analysis of the duration of mobile/cellular phone use was performed, it was found that the impact of short-term and medium-term mobile/cellular phone use on the risk of meningioma was statistically significant (OR: 0.83, 95%CI: 0.76-0.90, I²=39.5%, p=0.142 and OR: 0.83, 95%CI: 0.75-0.93, I²=32.3%, p=0.194, respectively), but not for long-term mobile/cellular phone use (OR: 0.91, 95% CI: 0.80-1.03, I²=0.0%, p=0.870). Hardell L., et al. (2008) conducted a meat-analysis on the regular use and long-term use of mobile/cellular phone, results of which are consistent with ours (OR: 0.8, 95%CI: 0.7-0.99 and OR: 1.3, 95%CI: 0.9-1.8, respectively), but there is no relevant analyses on short-term and median-term [31]. Lahkola A., et al. (2006) meta-analyzed the longest use of mobile phones of included articles, but found no statistically significant correlation (OR: 0.87, 95%CI: 0.72-1.05) [32].
Meningioma can cause epilepsy and neurological deficits caused by compression of adjacent nerve tissues through progressive enlargement, which is the most common tumor originating in the meninges [33]. The contribution of mobile/cellular phone use to the risk of meningioma may need to consider the synergistic effect of metal and RF-EMF. The correlation between radiation exposure and meningioma risk may be more affected by the age at the time of radiation exposure than the amount of exposure [34]. Considering that the latency period from radiation exposure to meningioma occurrence can be as long as 36 years [35], the definition of long-time exposure for meningiomas in the current researches is still not appropriate. Moreover, RF-EMF based on occupational exposure has not been shown to be associated with an increased risk of meningioma [36, 37]. The current evidence concerning the risk of meningioma and the use of mobile/cellular phones is relatively limited, and more long-term studies with large samples are still urgently needed.
In this meta-analysis, there was no statistically significant association between regualr use of mobile/cellular phone and acoustic neuroma (OR, 0.98; 95% CI, 0.76-1.25; I²=60.7%, p=0.013). When it comes to subgroup analysis, the impact of duration of use still has no statistical significance. There are also a few of meta-analysis studied acoustic neuroma. In 2008, L.Hardell published meta-analysis of nine studies on acoustic neuroma and yield (OR, 0.9; 95% CI, 0.7-1.1)
. But when it comes to use > or =10 years, the result showed positive effect on using mobile phone to the risk of acoustic neuroma (OR, 1.3; 05% CI, 0.6-2.8) [32]. However, they did not analysis the risk for all tumors. A. Bortkiewicz’ s meta-analysis in 2017 showed similar result as ours (OR, 0.96; 95% CI, 0.87-1.06), but they did not study the duration of using mobile phone and the risk of acoustic neuroma [38].
The followings are several limitations that may contribute to the result. Selection bias is a concern that the cases and controls may not be representative. For example, cases may be under ascertainment for the reason that they were diagnosed and treated outside study area or in some not-participating clinics. Also, people who use mobile phone regularly may have higher potential to participate, especially when the questionnaire is computer-assisted. Thus if mobile/cellular phone users in the control groups were more likely to participate than non-users, the risk may be underestimated. And few of the studies did not use blinding at interview. What should be noticed is that the dead who died of serious conditions were excluded and only survivals participated, which may also affect the result. What’s more, the number of studies in the meta-analysis is small, especially when it comes to subgroup analysis.
In conclusion, our study performed a meta-analysis on the association between mobile/cellular phone use and risk of gioma, meningioma and acoustic neuroma based on the duration of use. We found use of mobile phone can decrease the risk of meningioma, especially when the time since first use was between 0-5 years and 5-10 years, while the protective effect disappeared in longer term (more than 10/11 years). For glioma and acoustic neuroma, there were no statistical significance in our meta-analysis. More studies and more cases are needed to explore the possible influence of long-term use of mobile phone, and one standard protocol is also needed for large scale research.