BioEd Online

Using a mobile phone for ten or more years doubles the risk of getting a type of benign head tumour, a Swedish study has found.

The study is relatively small, it looked at 148 patients and 600 controls, and the effect will need to be confirmed with larger groups. But it is the first to show clear evidence that mobile phone use could increase the risk of getting tumours.

"We were surprised about the results, but the outcome is quite clear," says Anders Ahlbom, an epidemiologist at the Karolinska Institute, who was involved in the study.

"We are now convinced of the quite strong risk due to the use of mobile phones, and we are waiting for confirmation from the other research groups," says Ahlbom.

Sweden is one of the 13 countries taking part in the INTERPHONE study. This research programme, coordinated by the World Health Organization's International Agency for Research on Cancer (IARC) in Lyon, France, was set up in 1998 to investigate whether exposure to the radio-frequency electromagnetic fields from mobile phones causes damaging health effects.

Twice the tumours

The Karolinska team looked at the incidence of acoustic neuroma, a benign tumour that grows on the nerve connecting the ear to the brain. Normally the chance of developing acoustic neuroma is 1 in 100,000.

The researchers studied 148 acoustic neuroma patients and 604 healthy controls. 14 of the neuroma patients had regularly used mobile phones for over ten years, compared with 29 of the controls. That translates into a doubled risk of developing the condition, the researchers say.

All of the extra cases seemed to occur on the same side of the head to which the patients normally held their phone.

Danish comparison

The first results of the INTERPHONE study came in January from Danish researchers. Scientists from the Institute of Cancer Epidemiology in Copenhagen identified no link between phone use and the frequency of tumours, even though the average size of tumours that did occur was significantly larger for regular users than for nonusers.

But the Danish study was smaller than the Swedish one: it involved 106 acoustic neuroma patients and 212 healthy controls. Jorgen H. Olsen, head of the Danish institute, says that the Karolinska team's results are very convincing, and the differences in the outcome between the two studies, which used identical methodology, could be explained by the bigger sample size.

However, Olsen cautions that the Swedish results were partly based on asking the patients which side of the head they normally held their phone. People with a tumour on a particular side of the head might be more likely to say they held their phone on that side, he points out.

Studies are now complete in nearly all the countries involved in the INTERPHONE project, and the final results are expected to be released in early 2005, according to Elisabeth Cardis, chief of the radiation and cancer unit at the IARC.

Five of the countries involved in the project are also planning to start prospective studies following 250,000 people (50,000 in each country) to confirm any effects that INTERPHONE finds.