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Extremely low-frequency electromagnetic fields …

EPIDEMIOLOGYE xtremely low- frequency electromagnetic fields exposureand female breast cancer risk: a meta- analysis basedon 24,338 cases and 60,628 controlsChunhai Chen Xiangyu Ma Min Zhong Zhengping YuReceived: 8 January 2010 / Accepted: 30 January 2010 Springer Science+Business Media, LLC. 2010 AbstractExposure to Extremely low- frequency electro-magnetic fields (ELF-EMF) has been suggested to increasefemale breast cancer risk; however, the data have beeninconclusive. In order to derive a more precise estimationof the relationship, a meta- analysis was performed. Med-line, PubMed, Embase, the Cochrane Library and Web ofScience were searched. Crude ORs with 95% CIs wereused to assess the strength of association between ELF-EMF exposure and female breast cancer risk.

EPIDEMIOLOGY Extremely low-frequency electromagnetic fields exposure and female breast cancer risk: a meta-analysis based on 24,338 cases and 60,628 controls

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1 EPIDEMIOLOGYE xtremely low- frequency electromagnetic fields exposureand female breast cancer risk: a meta- analysis basedon 24,338 cases and 60,628 controlsChunhai Chen Xiangyu Ma Min Zhong Zhengping YuReceived: 8 January 2010 / Accepted: 30 January 2010 Springer Science+Business Media, LLC. 2010 AbstractExposure to Extremely low- frequency electro-magnetic fields (ELF-EMF) has been suggested to increasefemale breast cancer risk; however, the data have beeninconclusive. In order to derive a more precise estimationof the relationship, a meta- analysis was performed. Med-line, PubMed, Embase, the Cochrane Library and Web ofScience were searched. Crude ORs with 95% CIs wereused to assess the strength of association between ELF-EMF exposure and female breast cancer risk.

2 A total of 15studies published over the period 2000 to 2009 including24,338 cases and 60,628 controls were involved in thismeta- analysis . The results showed no significant associa-tion between ELF-EMF exposure and female breast cancerrisk in total analysis (OR= , 95% CI= ) and in all the subgroup analyses by exposure modes,menopausal status, and estrogen receptor status. This resultis in accordance with the previous meta- analysis carriedout by Erren in 2000. In conclusion, this meta-analysissuggests that ELF-EMF exposure has no association withthe susceptibility of female breast low-frequencyelectromagnetic fields Female breast cancer Meta- analysis Cancer riskIntroductionOver the past three decades, potential health effects ofexposure to electromagnetic fields have been extensivelyinvestigated in epidemiologic studies.

3 These studies havesuggested an association between occupational and resi-dential exposure to Extremely low- frequency electromag-netic fields (ELF-EMF) and cancer risk, and theInternational Agency for Research on Cancer evaluated theassociation in 2002 and concluded that ELF-EMF arepossibly carcinogenic to humans, based on the associationof higher level residential magnetic fields and increasedrisk for childhood leukaemia. The evidence for an associ-ation with breast cancer in women was, however, consid-ered to be inadequate [1].Breast cancer is the second most common cancer overallin the world and accounts for an estimated 16% of totalcancer among women. However, the etiology of breastcancer remains poorly understood.

4 The possible relationbetween ELF-EMF exposure and risk of breast cancer inwomen has received considerable attention and extensivelystudies. ELF-EMF are electric and magnetic fields withfrequencies ranging between 3 and 3000 Hz. ELF-EMFexposures may occur at work, through residential proxim-ity to electromagnetic field sources, or within homes, andthe primary exposure frequency is power frequency . Theubiquity of ELF-EMF in houses, offices, and factoriesmeans that nearly everyone is likely to be exposed to somelevel of ELF-EMF. Even a modest EMF-attributable breastcancer risk could thus result in a considerable number ofChunhai Chen and Xiangyu Ma contributed equally to this Chen M. Zhong Z. Yu (&)Faculty of Preventive Medicine, Department of OccupationalHealth, Key Laboratory of electromagnetic RadiationProtection, Third Military Medical University,Chongqing 400038, Chinae-mail.

5 MaFaculty of Preventive Medicine, Department of Epidemiology,Third Military Medical University, Chongqing 400038, China123 Breast Cancer Res TreatDOI analysis of the evidence regarding a possible asso-ciation between ELF-EMF and breast cancer is therefore ofinterest not only because it may contribute to a betterunderstanding of the etiology of breast cancer, but alsobecause of the public health implications if such an asso-ciation really date, epidemiologic studies of both residential andoccupational exposures to ELF-EMF and the risk of breastcancer have led to conflicting results. The most underlyinglimitation relates to difficulties in quantifying EMF expo-sure, as studies have often relied on proxy measures such asoccupational categories, wire codes, characteristics ofpower lines surrounding current and historical residencesrather than direct measurements of current fields as markersof past exposure.

6 In addition, details of the methods used toclassify exposures within these broad categories differedwidely. A meta- analysis of observational epidemiologicalstudies has previously been carried out by Erren [2] in 2000to examine the relationship between EMF exposure andbreast cancer. The pooled RR from the study in women (95% CI= ), and a fairly homogeneousincreased risk was found for men (RR= , 95% CI= ).Over the period 2000 2009, still extensively epidemio-logical studies have been carried out to investigate therelationship between ELF-EMF and breast cancer, espe-cially female breast cancer. Most of these studies are case control studies and focused on both residential and occu-pational exposure. Several studies have investigated the useof electric bed-warming devices as a potential source ofmagnetic field exposure.

7 Exposure levels for these differentstudies are usually measured according to the level of themagnetic field created in units of Gauss (mG; 1 Gauss=1000 mG) or Tesla (mT; mT=1 mG). These epide-miologic literatures, as summarized previously, haveyielded inconclusive results. It is still unclear whetherexposure to ELF-EMF is associated with female that the recent studies may have a high quality, itmight be important to reassess ELF-EMF exposure (both athome and at work) over the recent 10 years [3]. Our studyis a response to this. The purpose of the present investi-gation was to reassess the risk of female breast cancerassociated with ELF-EMF exposure in the light of theserecent publications. Thirteen case control reports focus onwomen are considered now.

8 Subgroup analyses were car-ried out further with respect to the exposure modes, men-opausal status and estrogen receptor (ER) status. This papersupplements an earlier meta- analysis on possible associa-tions between exposures to ELF-EMF and female breastcancer. In so doing we hoped to be able to provide answersto the following questions: Could the association betweenELF-EMF and female breast cancer be confirmed? Whatrecommendations can we make for further studies, ifwarranted?MethodsSearch strategy and selection criteriaThis study was performed according to the proposal ofMeta- analysis of Observational Studies in Epidemiologygroup (MOOSE) [4]. A comprehensive search strategy wasconducted towards the electronic databases includingMedline, PubMed and Embase, the Cochrane Library andWeb of Science using terms breast cancer , breastneoplasm , and electromagnetic fields over the periodJanuary 2000 to December 2009.

9 Reference lists of theidentified articles were also examined and the literatureretrieval was performed in duplication by two independentreviewers ( Chen and Ma).We reviewed titles and abstracts of all citations andretrieved literatures. The studies that met the followingcriteria were chosen: (1) the publication was a population-based case control study referring to the associationbetween ELF-EMF exposure and breast cancer in females;(2) all cases were first diagnosed as invasive or in situbreast cancer; (3) the papers must offer the size of thesamples, number of exposed and non-exposed individualsin cases and controls or other information that can help usinfer the results; (4) when multiple publications reported onthe same or overlapping data, we used the most recent orlargest population as recommended by Little et al.

10 [5];and(5) publication language was confined to extractionA number of different methods were used to measure ELF-EMF exposure in the studies examined. Some expressedexposure simply as a binary variable, exposed / notexposed , other reports were stratified according to mea-sured or assumed intensity or time-weighted average(TWA) of exposure to ELF-EMF. To aggregate exposurecategories across studies, we dichotomized exposure stratausing cut-off points. Although the specific cut-off pointsused for the epidemiologic analyses differed and the periodover which the TWA was estimated varied. Generally, cut-off points closest to , which were common to most ofstudies, were used in this was extracted from each study by two reviewers( Chen and Ma) independently according to thepre-specified selection criteria.


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