Hardell L, Hallquist A, Mild KH, Carlberg M, et al. (2002)

This study used a different set of patients from those used in the papers published by these authors in 1999 and 2000. Cancer registries were used to identify new cases of brain tumour, aged 20 to 80 years, from four medical regions of Sweden. The cases were diagnosed during the period January 1, 1997 to June 30, 2000. Initially 2,561 cases were identified, but after further investigation to confirm the diagnosis and after exclusion of deceased persons, 1617 cases remained. Each case was age and sex matched with a control from the same geographical region. Questionnaires were sent to each participant, and followed up by telephone interview if clarification of responses was needed. Questions were asked about a number of different exposures. Details were obtained about the type of phone used, as well as number of years used, mean number of minutes of use per day, and which ear was used most frequently.

The results were based on 1,303 matched pairs for whom complete information was available. There was an increased risk of brain tumour for analogue phones (OR of 1.3). This increased to 1.4 for those using phones for more than 5 years and to 1.8 for more than 10 years' use. Analysis of different tumour types showed no increase in risk for malignant tumours, but an increased risk for analogue phones for benign tumours. This latter finding was mainly due to an increased risk for acoustic neuromas (OR 3.5).
However, when other exposures were considered, the risks for >5 and >10- year users declined to non-statistically significant ORs of 1.1 and 1.3 respectively. Increased risk was found for cases with a tumour in the temporal area. This was true for cordless phone users of more than 5 years duration (OR 1.9) as well as those using analogue phones (OR 2.0; 1.9 and 2.6 for 5 and 10-year users respectively). When the side of the head of phone use was examined, unusual results were found. Not only was there an increased risk of brain tumour on the same side as phone use for analogue, digital and cordless phones, but this was true not only for tumours in the temporal areas, but also for other areas of the brain.

Other authors have failed to confirm these results. Inskip(2001) and Muscat (2000) did not find an increased risk of brain tumours with cell phone use, nor did they find evidence of increased risk on the same side as the phone was used. Muscat et al. (2002) did not find an increased risk of acoustic neuromas. The present study by Hardell and colleagues is the first to suggest an increased risk with cordless phones. In view of the discrepancies between the results of the papers published to date, the large-scale study conducted under the auspices of the International Agency for Cancer Research (IARC), whose results are expected in 2-3 years, is awaited with interest.