Per cansa.org, preliminary reporting by IARC in October 2008 (based on data from the Nordic countries and part of the United Kingdom), showed a significant increased risk for glioma on the side of the head associated to cellphone use of 10 years or more. However, the final results of the Interphone study on 17 May 2010 showed that no relative risk for glioma or meningioma was observed for persons with more than 10 years of cellular phone use.
An increased risk of brain cancer is not established from the data from Interphone. However, observations at the highest level of cumulative call time and the changing patterns of mobile phone use since the period studied by Interphone, particularly in young people, mean that further investigation of mobile phone use and brain cancer risk is merited.
Per cancer.org, "The measurement of cell phone use in most studies has been crude. Most have been case-control studies, which have relied on people’s memories about their past cell phone use. In these types of studies, it can be hard to interpret any possible link between cancer and an exposure. People with cancer are often looking for a possible reason for it, so they may sometimes (even subconsciously) recall their phone usage differently than people without cancer. With these limitations in mind, it is important that the possible risk of cell phone exposure continue to be researched using strong study methods, especially with regard to use by children and longer-term use."
A case-control study is a type of observational study design in which two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute. Case-control studies are often used to identify factors that may contribute to a medical condition by comparing subjects who have that condition/disease (the "cases") with patients who do not have the condition/disease but are otherwise similar (the "controls"). They require fewer resources but provide less evidence for causal inference than a randomized controlled trial since subjects are not randomized to the exposed or unexposed groups. Rather the subjects are observed in order to determine both their exposure and their outcome status and the results may be confounded by other factors, to the extent of giving the opposite answer to better studies. Randomized double blind placebo control (RDBPC) studies are considered the “gold standard” of epidemiologic studies since when they are well designed, they provide the strongest possible evidence of causation. Per Joel M. Moskowitz, epidemiologic research does not yield conclusive evidence and the quality of the epidemiologic research has been problematic on which one cannot draw causal inferences from case-control studies.
Numerous studies published so far have not found a link between cell phone use and the development of tumors. Also, three large studies such as the 13-country INTERPHONE study (the study found no link between brain tumor risk and the frequency of calls, longer call time, or cell phone use for 10 or more years), the Danish cohort study (Cell phone use, even for more than 13 years, was not linked with an increased risk of brain tumors, salivary gland tumors, or cancer overall, nor was there a link with any brain tumor subtypes or with tumors in any location within the brain), and The Million Women Study (found no link between cell phone use and brain tumors overall or several common brain tumor subtypes, but it did find a possible link between long-term cell phone use and acoustic neuromas) have had some important limitations that make them unlikely to end the controversy about whether cell phone use affects cancer risk. Another study in 2011 shows doubling of the risk of head tumours induced by long-term mobile phone use or latency.
The evidence so far is equivocal. Some studies have shown an overall increase in incidence among long-term users, some an increase in only certain histologic types of brain tumors, and some no increase at all or—oddly—a reduction in incidence. Two recent meta-analyses both came down on the side of suggesting that there may be evidence of a link. So far, no one seems to be able to muster much more conclusiveness than that.
Regarding the 2009 metanalytic study 'Cell phones and brain tumors: a review including the long-term epidemiologic data', "it is hard to know what to make of these findings because most studies by other researchers have not had the same results, and there is no overall increase in brain tumors in Sweden during the years that correspond to these reports."
Two Australian neuro-surgeons, Professor Vini Khurana and Dr Charlie Teo of the Australian National University, together with their team of epidemiologists and statistician, conducted an analysis of eleven studies of cell phone use. The results, published in The Surgical Neurology Journal Volume 72, Issue 3, concludes that significant statistical evidence suggests a link between prolonged cell phone use and the risk of developing brain tumours on the same side that the phone is used. However, they state that the studies incorporated in the meta-analysis relies on the participants recalling their cell phone usage through questionnaires and telephone interviews, and not through cell phone company records which could be viewed as biased.
Cardis and Sadetzky state that "There are now more than 4 billion people, including children, using mobile phones. Even a small risk at the individual level could eventually result in a considerable number of tumors and become an important public-health issue. Simple and low-coast measures, such as the use of text messages, hands-free kits and/or the loud-speaker mode of the phone could substantially reduce exposure to the brain from mobile phones. Therefore, until definitive scientific answers are available, the adoption of such precautions, particularly among young people, is advisable". Per W. K. Alfred Yung in 2010, "We have some hope that the questions about a cell phone–brain tumor link will be answered, eventually."