Primary CNS tumors in adults and environmental factors: an update

The incidence of adult primary brain tumors is increasing in some European countries. High-dose ionizing irradiation, rare genetic syndromes, and genetic predisposition in 5 % of families are a few established environmental risk factors for brain tumor. Mobile phone use that causes near brain exposure to radiofrequency electromagnetic waves and thus creates risks of CNS tumors has been the focus of many studies. Nine meta-analyses were available on this subject. The Interphone multi-center case-control study is the largest one to date; it included 2.708 glioma and 2.409 meningioma cases and matched controls in 13 countries. Studies exploring metals (cadmium, lead), pesticides, outdoor pollution, virus, and risk of glioma created by exposure to them were reviewed. Interphone study did not show increased risk of glioma or meningioma in mobile-phone users. One recent meta-analysis in 2017 found that prolonged exposure i.e.,> 10 years of all phone types was associated with increased risk of ipsilateral CNS tumor locations. In another meta-analysis, long-term use of mobile-phones was found to be a risk factor for low-grade glioma. In case of all durations regarding mobile phone use and both sides of the head, the results of pooling data were more discordant. A large prospective study in 2014 showed that long term use vs never use increased risks of acoustic neurinoma (10+ years: RR = 2.46, 95 % CI = 1.07-5.64, P = 0.03), but not of glioma or meningioma. Studies of other risk factors showed no/weak/contradictory association with brain tumor risk. In the absence of robust and consistent evidence, a causal relation between radiofrequency exposure and CNS tumors was not found. Large prospective studies of this kind regarding a disease with low incidence require a high number of participants and a long follow-up period.