To the Editor:
Neoplasms of the parotid gland and other salivary glands remain rare cancers and, although their incidence has increased in recent decades, relatively few risk factors have been identified.1,2 A recent study in Israel,1 based on ecologic data, found a 4-fold increase in the incidence of parotid malignant tumors between 1970 and 2006, and this increase was linked to the increased use of cell phones during that period. To assess whether these findings could be corroborated elsewhere, publicly available data for England from the UK Office of National Statistics for 1986-2008 was examined.3
The sex-stratified number of registered new cases (ICD-104) and directly age-standardized cancer registration rates per 100,000 people were obtained for malignant neoplasms of the parotid gland (C07) and for other and unspecified major salivary glands (C08). Registration rates specifically for malignant neoplasms of the submandibular and sublingual glands1 were not available.
Registration rates of malignant neoplasms of the parotid gland (Fig.) increased from 0.5 to 0.8 cases per 100,000 between 1986 and 2008 in men (test for trend P < 0.01) and from 0.4 to 0.6 per 100,000 in women (P ∼ 0.01). The number of new cases in this same period more than doubled from 112 new cases in 1986 to 247 in 2007 in men, and increased from 116 to 199 cases in women (eFigure, http://links.lww.com/EDE/A477). Whereas for men a gradual linear increase of an additional 4-5 cases per year (R2 ∼ 0.82) is observed, this is less clear for women (R2 ∼ 0.54). Registration rates of malignant neoplasms of other and unspecified major salivary glands remained stable in men and increased only slightly in women.
Compared with the trends in Israel,1 these data indicate a smaller, about 2-fold in absolute numbers of new cases, increase in parotid gland tumor incidence, with a trend more pronounced in men than women. To some extent the absence of a similarly large trend compared with Israel may be explained by a reported higher cell phone use in Israel compared with England.5 Nonetheless, while cell phone use in England, similar to other countries, has increased dramatically—with the number of subscribers increasing from about 50,000 in 1985 to over 52 million (91.17 per 100 people) in 20036—malignant neoplasms of the parotid gland still remain relatively rare. Moreover, these data suggest that the increase in incidence had already started before cell phones started to be used widely. It also seems unlikely that men and women use their cell phones very differently7 or that men are more susceptible to radio frequency exposure than women. These data suggest that another exogenous factor might be a more likely explanation. For example, alcohol consumption2 has been linked to tumors of the salivary glands, but in contrast to cell phone use has steadily increased in the previous decades, and is more frequent in men than in women.8
As with other registry data,1,7 the lack of data on both exposure and disease for individual persons prohibits drawing any conclusion on causal inference. INTERPHONE results from Israel5 indicated that subgroups with the highest use of cell phones have an increased risk of developing parotid gland tumors, but this risk could similarly not be observed at a population level. If, however, radio frequency exposure is related to cancer risk, it seems more likely that the exposure acts as a tumor promoter or inhibits the immune system, rather than being a cancer-initiating factor.7 This might explain the relatively small increase in parotid tumor rates compared with the exponential increase in cell phone use since the 1990s.
Although these data from England corroborate evidence from Israel that tumors of the parotid gland have increased in the previous decades, the trends in England started before widespread cell phone use, are more gradual, and differ in magnitude by sex, which does not point to cell phone use as the main driver of these trends—although, based on these data only, it cannot be excluded as a contributing factor either.
Frank de Vocht
Centre for Occupational and Environmental Health, Health, Sciences Research Group
School of Community Based Medicine Manchester Academic Health Sciences
Centre University of Manchester Manchester, United Kingdom
1. Czerninski R, Zini A, Sgan-Cohen HD. Risk of parotid malignant tumors in Israel (1970–2006). Epidemiology
2. Horn-Ross PL, Ljung BM, Morrow M. Environmental factors and the risk of salivary gland cancer. Epidemiology.
4. World Health Organization (WHO). International Statistical Classification of Diseases and Related Health Problems, 1992–1994.
Vol 1-3. 10th revision. Geneva: WHO; 1994.
5. Sadetzki S, Chetrit A, Jarus-Hakak A, et al. Cellular phone use and risk of benign and malignant parotid gland tumors-a nationwide case-control study. Am J Epidemiol.
7. De Vocht F, Burstyn I, Cherrie JW. Time trends (1998-2007) in brain cancer incidence rates in relation to mobile phone use in England. Bioelectromagnetics
. In press. Doi: 10.1002/bem.20648.