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Electromagnetic fields andfemale breast cancer
Maria FeychtingInstitute of Environmental Medicine,
Karolinska Institutet
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Breast cancer incidence
Source: Socialstyrelsens statistikdatabaser, Cancer Registry
0
20
40
60
80
100
120
140
160
180
200
1970 1975 1980 1985 1990 1995 2000 2005
No./100 000
Women
Men
Year
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Background
Hypotheses Magnetic field exposure suppresses
melatonin production (Stevens RG, 1987)
Melatonin protects against breast cancerdevelopment (Cohen M, 1978)
Therefore:
Magnetic field exposure increases breast cancer riskStevens RG, 1987
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Magnetic fields - melatonin
Contradictory evidence
Most human experimental studies found no
effect
Several observational studies have found
lower melatonin levels in exposed groups Often limited to subgroups
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Melatonin breast cancer, experimental
In vivo and in vitro experimental researchsupport protective effect of melatonin Effects of melatonin treatment have been
shown on MCF-7 breast cancer cells (estrogenreceptor positive)
Reduced incidence of chemically induced breasttumors after melatonin treatment
Increased incidence of breast tumors afterpinealectomy and chemical induction of breasttumors
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Melatonin breast cancer, humans
One prospective epidemiological studyfound no association
Travis et al. JNCI 2004
Another prospective epidemiological studyfound a lower breast cancer incidence in
women with high melatonin levelsSchernhammer et al. JNCI 2005
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Evaluations of EMF-breast cancer
The literature has been reviewed byseveral national and international bodies IARC UK AGNIR
and others
Conclusions: the available evidence isinadequate for an assessment
Most recent:
WHO Environmental Health Criteria
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IARC evaluation starting point
Performed in 2001 The epidemiologic evidence indicated little
or no overall effect
Some studies suggested an effect forpremenopausal breast cancer
Especially estrogen receptor positive, ER+
Fit the hypothesized biological mechanism
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Exposure sources
Occupational exposure Residential exposure
Electric bed heating devices, e.g.electric blankets
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Occupational exposure assessment
Early studies categorized job-titles intoelectrical occupations
Later studies have made personalmeasurements in occupations mostly onmen and created Job-Exposure-Matrices
(JEM)
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Occupational exposure assessment
Measurements on men may not adequatelyestimate magnetic field exposure for women differences between men and women holding
the same occupation,
no information about the exposure in typicallyfemale occupations - large proportion of womenwith unknown exposure levels
A Swedish study measured magnetic fields inoccupations common among women
Forssn et al. 2004
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Residential exposure assessment
Wire codes crude categorization based on proximity ofresidence to power lines of differentvoltages
Distance to power line alone no consideration of line voltage
Historical calculations Detailed information about power line
configuration and historical load
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Residential exposure assessment
Magnetic field measurements Spot measurements
Long term stationary measurements (24 or
48 h, even up to 7 days) Personal measurements
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Electric bed heating devices
Electric blankets, matress pads, waterbeds
Varying degree of information about habits
of use, duration of use, circumstances ofuse
Most sophisticated estimates in recent
studies
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New studies, occupational exposure
Crudeexposureassessment
No risk increaseoverallIncreased risk forER+ breast cancerafter 10 yr exposure
Interviews.Measurements onconveniencesample, six broadoccupational
groups
VanWijngaardenet al. 2001US
No dose-response
analyses
No risk increaseoverall
Increased risk forPR+ breast cancerwhen exp
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New studies, occupational exposure
Mix of ELFand RFfieldsNo controlof shift-work
Indication ofincreased breastcancer risk
Norwegian radioand telegraphoperators, no.years * type ofship
Kliukiene etal. 2003Norway
Crudeexposure
assessmentTime >0.1T
No risk increaseoverall
Census data every10thyear
Assessment byOccupationalhygienist
Kliukiene etal. 2004Norway
CommentResultsExp. assessmentStudy
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New studies, occupational exposure
Crudeexposureassessment
Increased risk inelectronic andelectric equipmentmanufacturers
Occupationalhistory. Exposureassessment basedon industry.
Peplonska etal. 2007Poland
Categorizedinto high,medium, low,backgroundexposure
No risk increaseLongest held full-time employment.Assessment byoccupationalhygienist
McElroy et al.2007US
CommentResultsExp. assessmentStudy
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Swedish occupational study
Case-control study 20,000 cases, 116,000 controls
Occupation from censuses every 5thyear
Exposure assessment: JEM developed for women based on
personal measurements
TWA, maximum exposure, rate of change Control of confounding from age, parity,
socioeconomic statusForssn et al. Am J Epidemiol, 2005
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Female JEM vs male JEM
Forssn, 2004
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Exposure contrasts
Large variation of exposure within many
occupations Identified occupations where a large
proportion of total measurements werehigh Cashiers, working proprietors in retail trade, air stewardesses,
dental nurses, cooks, post office clerks, kitchen maids
And occupations where a large proportionwere low e.g. farmers, primary-school teachers, in-office buyers and
sellers, general public administrative workers, national
insurance office workers
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Swedish occupational study
Results >0.3 TAll ages: 1.01 (0.93-1.10)
50 yr: 1.00 (0.90-1.11)ER+ tumors: 0.98 (0.87-1.11)
All risk estimates are close to 1.0regardless of age, ER-status, duration ofexposure, age at start of exposure etc.
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Occupations with exposure contrast
Overall results: OR=1.03 (0.94-1.13) 50 years at diagnosis: OR=1.06 (0.95-1.18)
ER+ tumors: OR=0.95 (0.84-1.08)
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Residential exposure
Highestquartile0.17 T,analyzedalso 90th
percentile
No indication of riskincrease, regardlessof age, ER-status orexposure metric
24 h bedroommeasurementsWire codes
Schoenfeldet al. 2003US, LongIsland
Lowexposurecutpoint,0.073 T
No indication of riskincrease, regardlessof age, ER-status orexposure metric
48 h bedroommeasurementsWire codes
Davis et al.2002US, Seattle
CommentResultsExp. assessmentStudy
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Residential exposure
Lack ofdose-response
Increased riskrelated to ever beingexposed to magneticfields >0.05 T
Historicalcalculations ofmagnetic fieldsgenerated bypower lines
Kliukiene etal. 2004Norway
Highestexposurecutpoint:0.4 T
No indication of riskincrease, regardlessof age, ER-status orexposure metric
7 day nighttimebedroommeasurementsWire codes
London et al.2003US, LA
CommentResultsExp. assessmentStudy
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Electric bed heating devices
Includes manyaspects ofuse that couldinfluencelevel of exp.
No indication ofrisk increase,regardlessof age or ER-status
InterviewVery detailedinformation aboutuse of electricblanket
Kabat et al.2003US, LongIsland
Investigatedalso otherappliances no association
No indication ofrisk increase
InterviewEver use andno. of hours/yearnot counting onlyto warm the bed
Davis et al.2002US, Seattle
CommentResultsExp. assessmentStudy
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Electric bed heating devices
Small numberof controls inhighest exp.categorySpeculatesthat African-American
women aremore sensitive
Increased risk,increasing withnumbers of yearsof use
Telephone interviewAny electricbedding deviceEver use andno. of yearsAnalyse separatelyonly to warm the
bed
Zhu et al.2003US,Tennessee
CommentResultsExp. assessmentStudy
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Summary and conclusions
More than a dozen additional studies afterIARC evaluation
Occupational studies: overall findingsnegative, but indications of increased risksin subgroups in some studies
No consistency regarding the subgroup inwhich increased risks were found
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Summary and conclusions
A large Swedish occupational case-controlstudy with enough power for statisticallystable analyses of the various subgroups
found no effects of the exposure.
Chance is a likely explanation for findings
of increased risks in different subgroupanalyses
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Summary and conclusions
Three well-designed residential studieswith comprehensive exposure assessmentfound no indications of increased risk
One Norwegian residential study found anincreased risk at very low exposure levels;
No obvious reason why this would not beseen also in the US studies should thefinding be true
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Summary and conclusions
Majority of studies of electric bed heatingdevices found no increased risk inludingtwo well designed studies
One study of African-American womenfound an increased risk speculates thatthis is a sensitive subgroup
However, African-American women werealso inluded in one residential study and noeffects were found
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Conclusions
The weight of the evidence available todaysuggests that power frequency magneticfield exposure is nota risk factor for
female breast cancer development
Cannot exclude possibility of minor risk
increase
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