Hardell L, Carlberg M, Hansson Mild K. Mobile Phone Use and the Risk for Malignant Brain Tumors: A Case-Control Study on Deceased Cases and Controls. Neuroepidemiology.35(2):109-114. Ahead of print. Jun 15, 2010.
The brain receives highest exposures to radiofrequency radiation during the use of mobile and cordless phones. Several studies, including those previously conducted by the authors, have shown an association between the wireless phone use and the risk of brain tumors. There was a concern that exclusion of deceased cases from the previous studies could bias the results.
The objective was to conduct a case-control study that would include patients who had died of malignant brain tumors before they could be interviewed by the investigators during the previous studies.
Cases (histologically confirmed malignant brain tumors diagnosed in the study area in 1997-2003 in individuals aged 20-80 years) were ascertained through the regional cancer registries. Two groups of controls were identified through the Death Registry of Sweden and matched to cases for year of death, gender, age and medical region. The first group of controls included individuals who had died of malignant tumors other than brain tumors, and the second group – individuals who had died from diseases other than cancer. The study included 464 cases, 464 controls that had died of malignancies other than brain cancer and 463 controls that had died of non-malignant diseases (for 1 case, a control could not be found). Exposure to mobile and cordless phones up to one year before the diagnosis (before the reference date for controls) was assessed by a questionnaire sent to relatives (spouses, parents, children or siblings).
The response rate was 75% for cases (n=346), 74% for cancer controls (n=343), and 60% for non-cancer controls (n=276). The overall odd ratio (OR) for mobile phone use calculated on the basis of the combined control groups was 1.3 (95% CI 0.9-1.9). It was 1.7 (95% CI 1.1-2.7) for >176 hours of mobile phone use, 3.4 (95% CI 1.6-7.1) for >2,000 hours, and 2.4 (95% CI 1.4-4.1) for latency of > 10 years. There was a significant (p=0.02) increasing trend in OR with increasing cumulative number of hours of mobile phone use. No significant increase in risk and no significant increasing trend with increasing cumulative hours of use were seen for cordless phones. Similar results were obtained when the risk was analyzed using the two groups of controls separately.
Interpretation and Conclusion
The results of this study show that exposure to mobile phones, but not to cordless phones, increases the risk of malignant brain tumors. The risk increases with latency and with cumulative number of hours of mobile phone use.