There is no link between the use of mobile phones and an increased risk of brain tumours, according to a 10-year Interphone study.
While some of the data in study, which was co-ordinated by the International Agency for Cancer Research (IARC), showed an increased risk for some mobile-phone users, the possibility of errors prevents researchers from drawing any hard conclusions.
Interphone is the biggest study so far on the possible link between brain cancer and mobile-phone usage.
The study - which has cost about €19.2m, including €5.5m from the telecom industry - was conducted in 13 countries, and included 2,708 glioma and 2,409 meningioma cases that were compared to healthy control cases.
Gliomas are a type of brain tumour arising in cells of the brain. Meningiomas arise from cells that make up the covering around the brain.
The overall results show no increased risk for either type of tumour among people who have used mobile phones regularly for more than 10 years, according to Maria Feychting, professor in epidemiology at Karolinska Institutet and in charge of the Swedish part of the Interphone study.
The overall conclusions of the report are also backed up by the fact that the number of cases of gliomas and meningiomas hasn't increased according to official Swedish cancer statistics, Feychting said.
Among the most heavy mobile-phone users, those who used their phones for more than 1,640 hours, the data suggest a 40 percent larger risk of getting a glioma tumor.
But potential errors in the data is a likelier explanation than is an actual increased risk, according to Feychting.
For example, some heavy users reported improbable usage patterns, including talking on the phone for more than 12 hours per day on average.
Also, getting to an increased risk only when reaching 1,640 hours of phone use isn't biologically believable, according to Feychting.
But she still thinks that these ambiguities warrant more research. A minority of the researchers also wanted to put more weight behind numbers that show an increased risk, Feychting said.
The methodology used by the Interphone study relies on participants remembering how many calls they have made, how long they talked and on what side they usually hold their phone, and that's hard to remember, according to Feychting.
In the end, the whole picture has to be looked at to validate the results and make a judgment call on what's believable, she said.
Problems related to the methodology can also explain why Interphone seems to suggest that using a mobile phone, in some cases, reduces the risk for brain cancer, according to the IARC.
A cohort study called COSMOS with participants in five European countries will try to get better data by, for example, relying more on information directly from mobile operators, according to Feychting.
Critics of the Interphone study have pointed out that it doesn't include children. The reason for excluding children is that a different method is needed for studying them from what is used for adults, according to Anders Ahlbom, director of the Institute of Environmental Medicine at Karolinska Institutet.
However, there is a need for further investigation of mobile-phone use and brain cancer risk among young people, according to Christopher Wild, director at the IARC.
Today, two ongoing studies are looking into this: MobiKids and CEFALO. The latter focuses on risk of brain tumors in children aged seven to 19 years, and researchers hope it will yield results during next year, according to Feychting.
Critics have also voiced concerns about the fact that other wireless phones, including ones based on the DECT (Digital Enhanced Cordless Telecommunications) standard, were excluded from the study. But they were included in the Swedish part of Interphone and no increased risks could be seen, Feychting said.
There is also the question of what repercussions mobile-phone usage will have longer term. Today, there is no data on usage periods longer than 15 years, according to Feychting.