Brain Tumor - Glioblastoma
Glioblastoma does not have a single definitive cause, but several factors have been identified (Weller 2013).
Men are about 50% more likely to develop glioblastoma than women (Davis 2016; Urbanska 2014; Ostrom 2014). Also, a woman’s risk goes up after menopause (Urbanska 2014). This finding, along with evidence that some gliomas express estrogen receptors, has led to the suggestion that hormones may play a role in the disease (Felini 2009; Andersen 2015; Lan 2017). However, much more research in this area is needed (Lan 2017; Urbanska 2014).
The chances of developing glioblastoma increase with age and peak at age 75 to 84 years (Ostrom 2013). Because the average lifespan of people in industrialized countries continues to increase, the median age when glioblastoma is diagnosed has risen to 64 years (Ostrom 2013; Thakkar 2014).
Heritage and Genetics
Glioblastoma is about twice as common in people with European-American ancestry than in those with African-American ancestry (Thakkar 2014; Urbanska 2014). Also, an increased risk of glioblastoma can be inherited within families. About 10 genetic mutations that increase risk of developing glioma have been identified, but most of them confer a relatively small increase in risk (Rice 2016). Glioblastoma may also result from genetic diseases such as tuberous sclerosis, Turcot syndrome, multiple endocrine neoplasia type IIA, and neurofibromatosis type I (Rice 2016; Urbanska 2014).
People who have been treated with radiation for medical conditions affecting their ears or skin have an increased risk of developing brain tumors (Bondy 2008; Hanif 2017). In addition, radiation to the head for childhood cancers is also a risk factor for brain cancer development later in life (Urbanska 2014; McNeill 2016; Alexander 2017). Some limited evidence suggests repeated CT scans of the head and neck region may increase glioma risk in some patients, although these findings have not been firmly established (Davis 2011).
Greater height has been associated with increased glioma and glioblastoma risk (Wiedmann 2017; Kitahara 2012). One study found that men over 190 centimeters (about six feet three inches) were about twice as likely to develop glioblastoma as men between 170 and 174 centimeters (Kitahara 2012). Interestingly, additional data suggest people who finished growing at a later age were more likely to develop gliomas (Little 2017).
Non-Ionizing Electromagnetic Radiation Exposure
Between the mid-1990s and early 2000s, the use of mobile and cordless phones increased rapidly (Carlberg 2014). These devices emit electromagnetic radiation from their antennas. Laboratory studies demonstrated that brain cells can be affected by electromagnetic fields (Xu 2017; Kaplan 2016). Whether mobile phone use is related to the development of brain tumors has been the subject of much debate (Urbanska 2014).
In 2011, the World Health Organization International Agency for Research on Cancer warned that the electromagnetic fields generated by mobile phones and other devices that emit similar non-ionizing electromagnetic radiation are “possibly carcinogenic to humans” (Baan 2011; IARC Working Group on the Evaluation of Carcinogenic Risks to Humans 2013; Carlberg 2014). This decision was based on data collected from human case-control studies (Carlberg 2014). A 2017 review and meta-analysis found that long-term mobile phone use (10 years or more) significantly increased the risk of glioma, but also emphasized that the available evidence is of low quality and more original research is needed before a better conclusion can be drawn (Yang 2017). Non-ionizing radiation emitted by cells phones doesn’t damage DNA directly, but researchers have proposed several other mechanisms by which cell phone radiofrequency waves may promote cancer (Havas 2017; Carlberg 2017). More research is needed to clarify the relationship, if any, between cell phone use and brain cancers.
Emerging evidence has explored whether a virus called cytomegalovirus (CMV) may be related to the development of glioblastoma (Dziurzynski 2012; Barami 2010). Approximately 50% to 80% of adults in the United States have been exposed to CMV, but relatively few have an active viral infection (CDC 2017). A study published in the New England Journal of Medicine described several important findings regarding the relationship between CMV and glioblastoma (Soderberg-Naucler 2013). Of the more than 250 glioblastoma patients, the authors detected the presence of CMV in all but one of the participants. Moreover, patients with lower numbers of virus-infected tumor cells survived 33 months on average, while those with higher numbers survived only 13 months. The authors speculated that CMV infection accelerated tumor progression (Soderberg-Naucler 2013; Rahbar 2013). Studies to validate this research have had mixed results, and researchers continue to study whether CMV has a role in the development of glioblastoma or whether it can affect the course of the disease (Garcia-Martinez 2017; McFaline-Figueroa 2017).