A large follow-up analysis of the complete Danish Cancer Registry showed no increased risk of tumors of the central nervous system (CNS), providing little evidence for a causal association.
The only cohort study investigating mobile phone use and cancer to date is a Danish nationwide study comparing cancer risk of all 420,095 people who had signed a mobile-phone contract with a phone company from 1982, when such phones were introduced in Denmark, until 1995, with the corresponding risk in the rest of the adult population with follow-up to 1996 and 2002. No evidence of any increased risk of brain or nervous system tumors or any cancer among these subscribers was found. People who had a subscription for more than 10 years were found to have a decreased risk of developing a tumor of the brain or nervous system, but this was based on only 28 cases.
Patrizia Frei, a postdoctoral research fellow for the Institute of Cancer Epidemiology, Danish Cancer Society (Copenhagen, Denmark), and colleagues followed participants in the mobile phone subscriber study to 2007, reporting their findings on BMJ.com (http://www.bmj.com/content/343/bmj.d6387.full.pdf). They subdivided all Denmark-born Danes 30 years and older into subscribers and nonsubscribers of cell phones before 1995. Among 358,403 Denmark-born subscription holders, 10,729 cases of CNS tumors were seen in the follow-up period of 1990-2007.
The investigators observed no overall increased risk for CNS tumors or for all cancers combined in mobile phone users. Among those who used cell phones the longest (13 years or longer), cancer rates were almost the same in both long-term users of mobile phones and nonsubscribers. No dose-response relation was uncovered, either by years since first cell-phone subscription or by tumor location in the head (for example, near where the phone is usually held to the head).
Although Frei and colleagues found no association between long-term use of mobile phones and heightened cancer risk, they pointed out that a small to moderate risk increase for subgroups of heavy users or after even longer induction periods than 10 to 15 years could not be ruled out.