From 1990 to 2007, 358
403 subscription holders beyond the first year of subscription accrued 3.8 million person years, with male subscribers providing nearly all person years (3.2 million). During follow-up, 122
302 cases of cancer occurred in men and 133
713 in women (table 1); in 5111 men and 5618 women these were tumours of the central nervous system.
Table 1 Overall incidence rate ratios (95% confidence intervals) for all cancers, smoking related cancers, and tumours of central nervous system among mobile phone subscribers in Denmark, 1987-95, followed up to 31 December 2007, for men, women, and (more ...)
The incidence rate ratio for all cancers was slightly decreased in men (incidence rate ratio 0.96, 95% confidence interval 0.95 to 0.98) but not in women (1.02, 0.98 to 1.06). When we restricted the outcome to smoking related cancers, the estimate in men was decreased (0.93, 0.90 to 0.96), decreasing to 0.87 (0.81 to 0.93) in people with 13 or more years of subscription. Further analyses showed that the decreased incidence rate ratio for smoking related cancers was restricted to men with basic or vocational training (0.91, 0.89 to 0.94). In the higher education group (men with >12 years of education), the association between mobile phone use and smoking related cancers was close to unity (1.01, 0.93 to 1.09), strongly suggesting a lack of confounding by smoking in this subgroup. For tumours of the central nervous system, the incidence rate ratio was consistently close to 1 in women and men, both overall and when stratified by years since first subscription, and also when restricted to men in the highest education group (table 1).
Analyses by morphological subtype of intracranial central nervous system tumours found a slightly but non-significantly increased incidence rate ratio for glioma in men (1.08, 0.96 to 1.22). The incidence rate ratio was highest in the shortest term users (1-4 years: 1.20, 0.96 to 1.22), and beyond five years of use numbers were only slightly raised, and there was no dose-response effect with increasing years of subscription (table 2). In women, there was no association between mobile phone subscription and glioma regardless of duration (table 2). For meningioma, there was a reduction in risk of 22% for male subscribers, with some variations by years of follow-up but again no indication of dose-response relation. In women, numbers were small, but there was no sign of increased incidence rate ratios for meningioma (1.02, 0.71 to 1.47). With regard to other and unspecified intracranial tumours of the central nervous system, estimates were non-significantly increased in men (incidence rate ratio 1.12, 0.95 to 1.33) and women (1.19, 0.85 to 1.67), but with no clear indication of a dose-response effect (table 2).
Table 2 Incidence rate ratios (95% confidence intervals) for intracranial tumours of central nervous system categorised according to ICD-O morphology and topography codes among men and women with mobile phone subscriptions in Denmark, 1987-95, followed (more ...)
Further subdivision of gliomas in men by site (table 3) showed a marginally increased incidence rate ratio for the temporal lobe (1.13, 0.86 to 1.48; n=65). When we stratified data by duration of follow-up, the highest estimates were seen in the periods 1-4 and 5-9 years of follow-up (incidence rate ratio 1.35, 0.83 to 2.20, n=18; and 1.31, 0.89 to 1.92, n=29, respectively), but decreased for subscribers of 10 or more years (0.81, 0.50 to 1.32, n=18). For other sites, the highest incidence rate ratio was found for the occipital lobe (1.47, 0.87 to 2.48, n=18), with the highest estimate for the shortest time users (1-4 years) (2.50, 1.18 to 5.31, n=8), and a non-significantly increased incidence rate ratio of 1.36 (0.57 to 3.23, n=6) for subscribers of 10 or more years. The incidence rate ratio for parietal lobe tumours was non-significantly decreased (0.73, 0.50 to 1.05, n=33). A significantly increased estimate was seen for “other and unspecified” sites (1.35, 1.05 to 1.75, n=77), which persisted when restricted to ≥10 years of exposure (1.44, 1.00 to 2.06, n=35). To further investigate this finding, we estimated the incidence rate ratios for each subgroup separately. The highest estimate was found for the cerebral ventricle (2.58, 1.08 to 6.15) but was based on only eight cases. Non-significantly increased incidence rate ratios were found for the unspecific groups “overlapping lesion of brain” (1.34, 0.92 to 1.95, n=35) and “brain, unspecified” (1.31, 0.86 to 1.99, n=29) respectively. In long term subscribers (≥10 years), incidence rate ratios for these groups were 1.48 (0.92 to 2.67, n=13) and 1.62 (1.00 to 2.60, n=21), respectively.
Table 3 Incidence rate ratios (95% confidence intervals) for gliomas by anatomical site among male mobile phone subscribers* in Denmark, 1987-95, followed up to 31 December 2007