The 10-year international survey found that extended use may increase the cancer risk.
Keith Srakocic / AP Enlarge
GENEVA - Cell phone users worried about getting brain cancer are not off the hook yet.
A major international study into the link between cell phone use and two types of brain cancer has proved inconclusive, according to a report due to be published in a medical journal tomorrow.
A 10-year survey of almost 13,000 participants found most cell phone use did not increase the risk of developing meningioma - a common and frequently benign tumor - or glioma - a rarer but deadlier form of cancer.
There were "suggestions" that using cell phones for more than 30 minutes each day could increase the risk of glioma, according to the study by the World Health Organization's International Agency for Research on Cancer.
But the authors added that "biases and error prevent a causal interpretation" that would directly blame radiation for the tumor.
Longer call times appeared to pose a greater risk than the number of calls made, the study found.
Among the factors not examined were the effects of using hands-free devices during calls or the risk of having cell phones close by, such as in a pocket or next to the bed at night, while not making calls.
The authors acknowledged possible inaccuracies in the survey from asking participants to remember how much and on which ear they used their mobile phones over the past decade.
Results for some groups showed cell phone use appeared to decrease the risk of developing cancers, something the researchers described as implausible.
The authors said further investigation is necessary before they can conclude with certainty that there is no link between cell phone radiation and brain cancer.
They said that is partly because use of the devices has changed considerably since the start of the study in 2000.
Scientists also are planning to examine whether cell phone use increases the risk of tumors in the ear's acoustic nerve and the parotid gland, where saliva is produced.
A separate study will look into the effects of cell phone use on children, who are believed to be more susceptible to the effects of radiation.
The paper was compiled by researchers in 13 countries, including Britain, Canada, France, Germany, and Japan, but not the United States. It will be published in the International Journal of Epidemiology.
Scientists interviewed 12,848 participants; 5,150 had meningioma or glioma tumors.
Almost a quarter of the $24 million required to fund the study was provided by the cell phone industry. WHO said steps were taken to ensure scientists' independence was protected.
The Mobile Manufacturers Forum welcomed the study: "The mobile phone industry takes all questions regarding the safety of mobile phones seriously and has a strong commitment to supporting ongoing scientific research."