Searching for the roots of brain cancer
In general, one main over 2 and 1 woman over 3 get cancer in their lifetime. A tumor occurs when a single cell accumulates 6 or 7 DNA alterations of particular genes: cancer genes. What determines those alterations? There are two schools of thought: one that identifies the root cause in the environment in which we live and in our lifestyle, and the other that attributes its origin to chance and therefore, ultimately, to misfortune. From a study of the European institute of oncology it seems that the most frequent and important genetic alterations for the development of the cancer, the chromosomal translocations, do not happen casually in the genome, but are predictable and due to the external environment.
However, as reported in the special number of Nature Outlook on brain tumors, with regard to brain tumors in particular, the probability increases with the age and if one underwent radiotherapy and in any case the chances are very low and lower than 1%.
Epidemiologists are unable to explain the causes of most brain tumors. They identified some genetic factors and an external cause: ionizing radiation. They excluded almost all environmental factors, including non-ionizing radiation, although mobile phones have not been completely eliminated.
The International Agency for Research on Cancer (IARC) reported that in 2012 there were 257,000 new cases of brain or nervous system cancer worldwide – an incidence of 3 cases per 100,000 people. Brain cancer is more common in whites and its incidence is higher in northern Europe, around 10 cases per 100,000, followed by the United States, Canada and Australia. Most of these tumors, around 80%, are glioblastoma multiforme (GBM).
There are two known risk factors for brain cancer. One is ionizing radiation. The other is a family story. People with certain inherited conditions that promote tumor formation, including neurofibromatosis and tuberous sclerosis, are a higher risk. However, these conditions cause only 5% of the gliomas.
However, it seems that environmental factors are not as influential on the incidence of brain tumors as it is for other tumors because carcinogens have to go through different obstacles to reach the brain which is very well protected compared to other organs.
A possible risk factor on which controls remain undecided are the radiofrequency electromagnetic fields generated by mobile phones. Studies on male rats exposed discontinuously to high levels of cell phone radiation for nine hours a day over a two-year period found an increase in the incidence of a rare and reserved non-lethal tumor type in the heart of animals.
Since the use of mobile telephony in the late 1990s, a slight increase in the incidence of brain cancer has been reported in the United States but rates are not increasing enough to be able to claim that electromagnetic radiation due to the use of mobile phones increases the risk of a glioblastoma.
There is also no known physical mechanism by which non-ionizing radiation, which imparts much less energy than the ionizing counterpart, could damage DNA. However, the increase of use of mobile devices makes it useful to continue this search.
Certain conditions, including allergies, diabetes and chicken pox, seam to reduce a person’s risk of getting a brain tumor. People found to be positive for the immunoglobulin-E (IgE) antibody were found to have 25% less chance of developing a glioma. The women whose blood contained IgE have halved risk of getting a glioblastoma. One hypothesis is that the immune system, already on alert for the presence of allergens, is somehow able to stop brain cancer. Another possibility is that people with strong allergic reactions are more effective in eliminating carcinogens before these cause brain problems.
Several other studies have found similar results and it seams that to have a history of respiratory allergies is reducing a person’s risk of glioblastoma of about 30%.
The presence of an inverse relationship between the levels of glioma and glycaemia in people with diabetes seems to be confirmed. It seems even if it is not yet confirmed that metformin, a drug that is regularly prescribed to treat diabetes, can also stop some processes involved in tumor growth.
Another result that emerged is that contracting chickenpox reduces a person’s glioma risk by 21%. It is not clear whether the varicella-zoster vaccine used to prevent chickenpox has the same effect on the risk of developing glioma, but if so, vaccination could be recommended to help prevent brain cancer as well as the vaccine against Papilloma virus is used to reduce the risk of developing cervical cancer.
Hence the root is probably an interaction between genetics, environment and lifestyle, but maybe it’s just bad luck. However we must be sure because if we could find something, maybe we could try to intervene.