Incidence trends of malignant parotid gland tumors in Swedish and nordic adults 1970 to 2009.

To the Editor: Salivary gland tumors are relatively rare, accounting for 2–5% of all head and neck tumors in various countries, with the most common subtype (75%) being parotid gland tumors. Ionizing radiation exposure is the only established risk factor to date. Recent studies have reported an increased incidence of malignant parotid gland tumors during the last decades, especially in Israel, but also in England. This has been speculated to reflect the increased prevalence of mobile phone use since the 1990s, from virtually 0 to close to 100%, considering the high exposure of parotid gland during mobile phone use. The Nordic countries were among the first to adopt mobile phone technology in the general population. We aimed to investigate incidence trends of malignant parotid gland tumors and all malignant salivary gland tumors in Sweden and in the Nordic countries, using the national registers. Patients 20 years or older with primary diagnosis of parotid gland neoplasms (ICD-7 International Classification of Diseases, Seventh Revision , 1420) and of salivary gland malignancies (ICD-7, 142) from 1 January 1970 to 31 December 2009 were identified from publicly available data in the Swedish Cancer Registry (http://192. 137.163.49/sdb/can/val.aspx) and the NORDCAN database (http://www-dep. iarc.fr/NORDCAN/English/frame.asp). We used direct standardization to calculate annual age-standardized incidence rates (cases per 100,000 person-years) using the world standard population. In Sweden, 3604 salivary gland tumor cases in adults 20 years or older were identified during the period 1970– 2009, of whom 2624 (73%) were malignant neoplasms of the parotid gland. The incidence of parotid gland tumors in Sweden decreased slightly during the early study period (Figure), and then remained stable for both sexes (0.9/ 100,000 person-years in 1970 and 0.8/ 100,000 person-years in 2009 for men; Supported by internal funding from the Institute of Environmental Medicine, Karolinska Institutet. M. Feychting is national principal investigator for the Swedish component of the Interphone study, which was funded in part by the International Agency for Research on Cancer, which was funded in part by the International Union against Cancer, which received funds from the Mobile Manufacturers’ Forum and the GSM Association. A. Ahlbom and M. Feychting are coinvestigators for the COSMOS study of mobile phone use and health, the Swedish part of which is funded by the Swedish Research Council, the Swedish Council for Working Life and Social Research, AFA Insurance, and VINNOVA, the Swedish Governmental Agency for Innovation Systems. VINNOVA received funds for this purpose from TellaSonera, Ericsson AB, and Telenor. Industry funding was given under agreements that the studies be given complete scientific independence. A. Ahlbom and M. Feychting are, or have been, members of the International Commission on Non-Ionizing Radiation Protection, an independent body setting guidelines for nonionizing radiation protection. They also serve as advisers to a number of public advisory and research steering groups concerning the potential health effects of exposure to nonionizing radiation. None of the authors has had assignments for the telecom industry. The authors reported no other financial interests related to this research. Copyright © 2012 by Lippincott Williams & Wilkins ISSN: 1044-3983/12/2305-0766 DOI: 10.1097/EDE.0b013e31825988fa FIGURE. Incidence trends of parotid gland tumors and salivary gland tumors in Sweden and Nordic countries combined from 1970 to 2009. Letters Epidemiology • Volume 23, Number 5, September 2012