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Mobile phones and cancer

Study
Results
Comment


Many of us use mobile telephones to a greater or lesser extent. Because mobile phones emit radio frequencies that can penetrate several centimetres into the human brain, it has been hypothesised that their use could possibly lead to tumours of the head and neck.


This possibility has led to a number of 'scare' stories in the popular press. Typically, debunking the scare involves trying to prove a negative, never an easy thing at the best of times. About the only way to prove a negative is to have very large amounts of data, but also demonstrating the lack of any sort of dose-response as well as no biological plausibility. A large Danish study goes most of the way to doing that for mobile phones and cancer [1].


Study


In the period 1982 to 1995 over 700,000 Danish citizens subscribed to a mobile telephone service. After eliminating those in which individual users could not be identified because they were corporate subscriptions, had incorrect addresses, were from Greenland or the Faroe islands, had a history of previous cancer, or were under 18 years, the final cohort consisted of 420,000 identified subscribers.


Because Denmark has a system of personal identification numbers, cohort members could be linked to files of a cancer registry that is virtually complete, and using a nationwide system of cancer classification. Follow up began from the first day of subscription, and ended on date of diagnosis of any cancer, death, emigration, or end 2002.


Numbers of cancers found were compared with the number expected in the general Danish population, for men and women, and in five-year age groups. Mobile phone subscribers were omitted from this comparison group.


Results


Most (85%) of the 420,000 subscribers were men. The median time of mobile telephone subscription was 8.0 years. Mobile subscribers had 14,250 cases of diagnosed cancer, against an expected number of 15,000, giving an overall standardised incidence ratio of 0.95 (95% confidence interval of 0.93 to 0.97).


For men and women analysed separately there was no difference from expected in all brain and nervous system cancers, or cancers of the salivary glands or eye. For men and women analysed together, there was no increased risk of any type of intracranial cancer, with a hint of a decreased risk for parietal lobe tumours. There was no increase in brain and nervous system tumours and leukaemias according to time from first subscription (Table 1).



Table 1: Brain and nervous system cancers, and leukaemias, by years of mobile phone subscription, compared with non-subscribers in Denmark



Standardised incidence rate
(95%CI)
Years of subscription
Person years
Brain and nervous system
Leukaemia
<1
420,000
0.9 (0.7 to 1.2)
1.1 (0.8 to 1.5)
1-4
1,656,000
1.0 (0.9 to 1.2)
1.1 (0.9 to 1.2)
5-9
1,327,000
1.0 (0.8 to 1.1)
0.9 (0.8 to 1.1)
≥10
170,000
0.7 (0.4 to 0.95)
1.1 (0.7 to 1.5)



There was no increased risk of any other type of cancer for men, with hints of decreased risk for lung, bladder, buccal, oesophageal and liver cancers, as well as other cancers and unspecified cancers. For women the numbers of individual cancers were small, and none had any large increase or decrease in incidence over expected.


Comment


What is good about this study is that it was large, of long duration, covered a whole population, and was performed in Denmark. Denmark has an almost unique ability to successfully link different databases through the use of personal identification numbers.


The results all but eliminates the concept that the use of mobile phones can cause cancer. And not just cancer, because the study allows detailed diagnosis of particular cancer types, including acoustic neuromas and cancers of temporal and parietal lobes which would be the parts of the brain closest to a mobile phone antenna, and hence most at risk.


The paper has a wonderful discussion, which not only puts these results into the context of others, but tells us that the authors could find no studies indicating any biological plausibility for a link between mobile phones and cancer. This comes a close to proving a negative as we are ever likely to get, but even more data will come out in future from continuation and extension of the study.


If you Google mobile phones and cancer, you will find links to over nine million sites. Some are good, some are up to date, but many are not. They should all reflect on the data from Denmark.


Reference:

  1. J Schüz et al. Cellular telephone use and cancer risk: update of a nationwide Danish cohort. Journal of the National Cancer Institute 2006 98: 1707-1713.

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