Wednesday May 14 2014
Primary brain tumours are uncommon
“Intensive mobile phone users at higher risk of brain cancers, says study,” The Guardian reports.
The news is based on a French study which identified 447 adults who were diagnosed with the most common types of brain tumour (meningiomas or gliomas) between 2004 and 2006. It matched them with 892 people who hadn’t been diagnosed with cancer, and interviewed both groups on their use of mobile phones.
Researchers found no association between regular mobile phone use (phoning at least once a week for six months or more) and risk of the brain tumour. However, it did find an increased risk of gliomas with the highest cumulative lifetime call duration (above 896 hours).
Not many people actually used their mobiles for above 896 hours – only 37 cases and 31 controls. When conducting analyses involving such small numbers of people there is an increased risk of chance findings.
Importantly, mobile phone use by these middle aged French adults 8-10 years ago is unlikely to reflect use today. Mobile use has become much more widespread (only 50% of adults being regular users in this study), and the extent of mobile use and pattern of use – particularly among younger people – has almost certainly changed.
For example, the study didn’t consider text messaging, which many use rather than calling directly, and this may reduce patterns and levels of exposure. This study also did not include smartphones (launched in 2007) which make use of 3G and Wi-Fi signals.
Arguably the study only provides information about mobile phone use from a decade ago and contributes little in the way of conclusive answers about the current picture.
Where did the story come from?
The study was carried out by researchers from Université Bordeaux Segalen in France, and was supported by grants from various French health and research organisations. The study was published in the peer-reviewed journal of Occupational and Environmental Medicine.
The Guardian and the Mail Online's reporting is generally representative of the findings of this study, although there are important limitations to bear in mind. Not least its relatively small size and the fact it used data from eight to 10 years ago. This is an important point to bear in mind when dealing with such a fast-moving technology as mobile phones. Show a teenager today a mobile phone from 10 years ago and they would consider it to be a museum piece.
The Mail also mentions that there was a significant association between heavy mobile phone use (more than 15 hours per month) and glioma. While this is technically true, in statistical terms the association only involved 29 cases and 22 controls. This greatly reduces the “statistical power” of the association (and there was no association with meningioma).
What kind of research was this?
This was a case control study conducted across four areas of France between 2004 and 2006, which looked at the association between mobile phone use in adults, and “primary tumours” of the brain or spinal cord. A primary tumour is one that started in that part of the body – as opposed to “metastatic tumours”, which spread from cancers in other parts of the body.
Principally they were looking at the association with two types of tumours:
- gliomas, which are the most common type of primary brain tumour and comprise several different types depending on cell type
- meningiomas which account for around a quarter of all brain tumours and develop from the layers that cover the brain and spinal cord
The researchers say that to date the potential cancer-causing effects of radiofrequency electromagnetic fields have been an area of much debate and controversy.
What did the research involve?
In this study, called CERENAT, the researchers identified people diagnosed with brain tumours (“cases”), and matched controls without brain tumours from the electoral role. They then collected information on mobile phone use from face-to-face questionnaires to look at the association.
The researchers identified all people over the age of 16 years, living in one of four French areas, who were diagnosed with a primary cancerous or benign tumour of the central nervous system (gliomas and meningiomas only) between June 2004 and May 2006.
They were identified through medical practitioners and population-based cancer registries. For each “case”, two controls without tumours of the central nervous system were identified, matched for age, sex and place of residence.
The researchers collected information on mobile phone use of the cases and controls using questionnaires administered in person. These questionnaires covered sociodemographic characteristics, medical history, lifestyle and detailed occupational and environmental data.
The questionnaires included a set of questions on mobile use and were completed by all “regular users” – defined as phoning at least once a week for six months or more. They included questions on mobile phone model, start and end dates for use of the phone, average number and duration of calls made and received per month, and whether personal or occupational, shared or individual use, or hands-free.
Potential confounders the researchers considered included level of education, smoking and alcohol consumption, occupation (including exposure to pesticides, electromagnetic fields and ionising radiation).
In their analyses, the researchers then looked at phone use in the year before the date of the tumour diagnosis.
What were the basic results?
There were 447 cases (253 gliomas, 194 meningiomas) and 892 controls. The average time between tumour diagnosis and interview was six months. Average age of the “cases” was 56 years for gliomas and 60 for meningiomas.
Half of the study population reported regular mobile use – with a third being occupational users. The average cumulative lifetime duration of calls was 115 hours, and average calling time 2.7 hours per month. It was also reported by the same number of cases and controls – 55% of glioma cases and controls, and 44% for meningioma cases and controls.
Compared with non-use, regular use of mobile phones was not significantly associated with risk of either of the brain tumours (odds ratio [OR] 1.24, 95% confidence interval [CI] 0.86 to 1.77 for gliomas; and OR 0.90, 95% CI 0.61 to 1.34 for meningiomas).
People with the highest cumulative lifetime duration of calls (above 896 hours) were found to be at increased risk of glioma (OR 2.89, 95% CI 1.41 to 5.93) and meningioma (OR 2.57, 95% CI 1.02 to 6.44) compared with never-users. People who made the highest cumulative number of calls (above 18,360) also had increased risk of glioma (OR 2.10, 95% CI 1.03 to 4.31), but there was no significant association between number of calls and meningioma.
How did the researchers interpret the results?
The researchers conclude that their data, “supports previous findings concerning a possible association between heavy mobile phone use and brain tumours”.
This French case-control study finds no association between regular mobile phone use (defined as phoning at least once a week for six months or more) and risk of the most common types of brain tumour. However, it does find increased risk with the heaviest use (cumulative lifetime call duration above 896 hours).
There are important considerations to bear in mind:
- This study is only representative of people diagnosed with brain tumour in these four regions of France between 2004 and 2006, and their matched controls. They may not be representative of all mobile phone users in France or elsewhere. The average age of people in this study was 56 to 60, and the study was also conducted eight to 10 years ago. In 2004 to 2006 mobile phones had perhaps been regularly used by the public for at most 10 years or less. The extent of mobile phone use by these middle aged people eight to 10 years ago, may not be comparable to younger people today who have greater cumulative years of mobile phone use now behind them, and now have further decades of use ahead of them.
- Another point to consider is that the current pattern of use in young people may also have changed. Due to the costs of calls many young people now communicate using texting or messaging apps. Also most smartphones use 3G (or in some cases 4G) and Wi-Fi signals so the pattern of exposure may have significantly changed.
- No association was found between brain tumour and regular mobile use. However an association was found between cumulative lifetime exposure of above 896 hours and tumours, very few people in this study actually reported this extensive use – only 24 glioma cases and 22 controls, and 13 meningioma cases and nine controls. When conducting analyses involving such small numbers of people there is an increased risk of chance findings.
- While the researchers have attempted to adjust for various potential lifestyle and sociodemographic confounders, there may still be other factors involved in this relationship, meaning it is difficult to prove cause and effect.
Overall, this study contributes little in the way of conclusive answers. It tells us more about mobile phone use a decade ago than today, and this may be of questionable value with such rapidly evolving technology.
What is required is an ongoing long-term cohort study into mobile phone use. Thankfully, we have one. The COSMOS study (a cohort study into mobile phone use and health) has now recruited 290,000 participants across five European countries including the UK.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.