There was no substantial change in brain tumour incidence among adults 5 to 10 years after cell phone usage sharply increased, according to a new brief communication published online in the Journal of the National Cancer Institute.

Although cell phone use has been proposed as a risk factor for brain tumours, a biological mechanism to explain this association is not known.

Isabelle Deltour, Ph.D., of the Institute of Cancer Epidemiology, Danish Cancer Society, in Copenhagen, and colleagues analyzed annual incidence rates of glioma and meningioma among adults aged 20–79 years from Denmark, Finland, Norway, and Sweden. Researchers identified 60,000 patients who were diagnosed with these types of brain tumours between 1974 and 2003.

The researchers found that incidence rates over this 30 year-period were stable, decreased, or continued a gradual increase that started before the introduction of cell phones. They also found no change in incidence trends in brain tumours from 1998 to 2003. The authors say this finding may be due to one of several reasons: that the induction period relating cell phone use to brain tumours exceeds 5–10 years; that the increased risk in this population is too small to be observed; that the increased risk is restricted to subgroups of brain tumours or cell phone users; or that there is no increased risk.

The authors did not assess cell phone usage at the individual level during this time period, only brain tumour incidence.

“Because of the high prevalence of mobile phone exposure in this population and worldwide, longer follow-up of time trends in brain tumour incidence rates are warranted,” the authors write.