Autores

Ahlbom A, Feychting M, Green A, Kheifets L, Savitz DA, Swerdlow AJ, ICNIRP (International Commission for Non-Ionizing Radiation Protection) Standing Committee on Epidemiology. Epidemiologic evidence on mobile phones and tumor risk: a review. Epidemiology 20(5):639-652.

Background

The increase in mobile phone use has generated concerns about safety.  The focus of this review, and that of many studies, is brain tumours and other sites in the head and neck close to mobile phone use. The authors discuss methodological features of the studies in this field that should be considered in interpreting the results. For example, the characteristics of exposure to radiofrequency fields (RF) depend on the mobile phone system and phone model, as well as on whether exposure was self-reported or based on billing record information. Studies that assess tumour risk based on whether the tumor is on the same side of the head as the phone is typically held may be subject to reporting bias. Because mobile phones are a relatively new technology, data on exposures more than 10 years before cancer diagnosis, which may be most relevant to cancer risk, are still limited. Lastly, studies differ in how cases and controls are defined, and in participation rates.

Objective
The objective of this review was to summarize the epidemiological evidence on mobile phone use and head and neck tumours.

Methods of Studies
The studies included in this review were conducted in 10 countries and are classified into four groups: (1) early studies conducted in the US; (2) studies conducted in Scandinavia by the Hardell group; (3) studies conducted within the Interphone collaboration, a series of 16 coordinated case-control studies conducted in 13 countries; and (4) independent studies, comprising 2 Nordic studies and 1 German study.  Only 2 studies have been cohort studies, the rest have been case-control studies.  All studies were limited to adults.  Due to differences in when cases were ascertained, lifetime exposure prevalence among controls has ranged from <10%-65%.  In addition, exposure definitions were inconsistent across studies.

Results and Interpretation
Glioma:  Among the 14 studies addressing the risk of glioma, all except 2 found no association with ever use of mobile phones. Similarly, most studies found no evidence for an association based on duration of use or cumulative exposure. Null or negative results could be caused by exposure misclassification or by differential participation rates among cases and controls.  However, in the authors’ view, it is more likely that subtle aspects of data collection and methods of analysis in the 2 positive studies explain the deviation in results.

Meningioma: Eleven case-control studies, 1 cohort study, and 2 pooled analyses have investigated the association between mobile phone use and meningioma, and all but the most recent found risk estimates close to or below unity. A particular consideration in the meningioma studies is the long time it takes for these types of tumours to develop. Thus, the negative findings are less convincing for this tumour type than for gliomas.
Acoustic Neuroma: The 13 original studies on acoustic neuroma generally included small numbers of cases, and all studies except the 2 most recent found risk estimates close to or below unity.  Acoustic neuroma is a slow-growing tumour and it is unlikely that recent exposure would affect tumour risk. Therefore, it is still unclear as to whether there are raised risks beyond 10 years from initial use.

Salivary Gland Tumours:  There is no consistent evidence of an increased risk of salivary gland tumours among mobile phone users, based on 4 case-control studies and 1 cohort study.

Conclusions
In the authors’ opinion, overall, the studies published to date do not demonstrate a raised risk within 10 years of mobile phone use for any brain tumour or any other head and neck tumour.  However, some key methodologic problems remain. Moreover, there is limited data on long latency and long-term use, which hampers conclusions about slow-growing tumours.  



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