Based on 11,892 observations of meningioma, LGG, and HGG, no general trend could be seen concerning increased income and increased risk of these CNST types. Data from these analyses must be interpreted with caution since the distribution of patients based on the above assumptions resulted in few observations in the group of high income.
Our results are in some context contradictory to the available data from the literature. It is concerning that the role of SES is known to be associated with the risk of many different cancer types, through various mechanisms [
4‐
6]. Lung cancer is an example of a disease which is more common in smokers than in non-smokers and since low SES is associated with a higher prevalence of smoking, lung cancer is more common in low SES groups [
5]. On the other hand, some cancer types such as early-stage prostate and breast cancer are discovered more in high SES groups because they often have better access to cancer screening and health care [
7]. For gliomas, no clear occupational or exposure risk factors have been identified, although some possible risk factors such as cellular telephone use are still controversial [
8]. Most patients with gliomas have no history of previous exposure to ionizing radiation, which is considered to be a risk factor for developing the disease [
10]. There have been studies suggesting that people in certain occupations, such as physicians are at increased risk of glioblastoma, but the results from these studies have not been convincing enough for any definitive conclusions to be made [
11].
The link between SES and incidence of gliomas has been previously thoroughly investigated. In an American study, data from the SEER (Surveillance, Epidemiology and End Results) Program was used to identify over 26,000 patients diagnosed with glioblastoma between 2000 and 2010 [
12]. When comparing SES based on census tract of residence, it was found that higher SES was strongly associated with increased risk of glioblastoma (
p < 0.001). Relative to patients in the lowest SES quintile, the highest SES quintile had a rate ratio of 1.45 (95% CI 1.39–1.51). In a similar study of SEER data for all glioma cases in adults > 25 years of age reported between 2000 and 2006, higher socioeconomic position based on county of residence was found to be statistically significantly associated with a higher incidence rate of glioma [
13]. Patients in the highest socioeconomic position quartile had a glioma risk rate of 1.14 (95% CI 1.39–1.51) times that of the first quartile. In a study including 880 patients with glioblastoma treated at a single neurosurgical unit in the UK, socioeconomic data were obtained at ward level from government sources [
14]. It was found that increasing incidence of glioblastoma was associated with increasing wage (
p = 0.044), less unemployment (
p = 0.0002), Indices of Multiple Deprivation (
p = 0.05), lower population density (
p = 0.0015), and greater ownership of cars (
p = 0.0005). A population-based case–control study of 321 meningioma cases, 494 glioma cases, and 955 controls was carried out in Sweden between 2000–2002, and it was found that a family income in the highest quartile was associated with an increased risk of glioma (OR 1.5, 95% CI 1.1–2.1) [
15]. However, socioeconomic factors were not associated with the risk of meningioma. In another case–control study by Inskip et al. of 489 glioma cases, 197 meningioma cases, 96 acoustic neurinoma cases, and 799 controls treated in three hospital in the USA between 1994 and 1998, the results showed a positive association with increasing household income for the risk of low-grade glioma, meningioma, and acoustic neurinoma but not for high-grade glioma [
16]. Similarly, positive associations were observed with level of education for low-grade glioma and acoustic neuroma, but not for high-grade glioma or meningioma. In a separate study, patients were interviewed regarding their use of handheld cellular phones [
17]. As compared with patients who had never, or very rarely, used a cellular telephone, the relative risks associated with a cumulative use of a cellular telephone for more than 100 h was not significantly elevated for any of the tumor entities. Neither did tumors occur disproportionately often on the side of head on which the telephone was typically used. These results are in line with the results from the large multinational INTERPHONE case–control study that included 2708 gliomas, 2409 meningiomas, and matched controls from 13 countries which showed no increase in risk of glioma or meningioma with use of mobile phones [
18]. One hypothesis regarding the increased glioblastoma risk in persons with high SES is related to cellular telephone use. Before the almost universal use of cellular telephones seen nowadays, the first users of the technology in the 1980s tended to be people who could afford buying a cellular phone, that is, people of high SES levels. However, the results from several large well-designed studies such as INTERPHONE [
18] contradicts this explanation, and it seems that the reason for higher incidence of gliomas in high SES groups is to be found elsewhere.
In conclusion, the results should be interpreted with caution, but there does not seem to be a correlation in this material between increased income and development of meningiomas, nor LGG or HGG.