Abstracts of epidemiological studies on female breast cancer
Studies of residential exposure
Int J Epidemiol. 1982 Dec;11(4):345-55.
Adult cancer related to electrical wires near the home.
Like childhood cancer, adult cancer was found to be associated with high-current electrical wiring configurations (HCCs) near the patient's residence. Such wiring can expose occupants of the residence to alternating magnetic fields (AMFs) at a level which, though very low, may produce physiological effects. Several patterns in the data suggest that HCCs and cancer may be causally linked: (1) a dose-relationship was found. (2) The association did not appear to be an artefact of age, urbanicity, neighbourhood, or socioeconomic level. (3) The association was most clearly demonstrable where cancer caused by urban/industrial factors was least apt to obscure the effect. (4) A distinct pattern of latency between first exposure to the HCC and cancer diagnosis was seen, which is consistent with a hypothesis of cancer promotion produced by AMF exposure.
Br J Cancer. 1986 Feb;53(2):271-9.
Mortality of persons resident in the vicinity of electricity transmission facilities.
Several studies have raised the possibility that exposure to electrical and/or magnetic fields may be injurious to health in particular by the promotion or initiation of cancer. To investigate whether the electricity transmission system presents a long term hazard to public health, the mortality of nearly 8,000 persons, identified as living in the vicinity of electrical transmission facilities at the time of the 1971 Population Census, has been followed to the end of 1983. All identified transmission installations within pre-defined areas were included in the study with the result that the greater part of the study group were believed to be resident near relatively low voltage sub-stations. Overall mortality was lower than expected and no evidence of major health hazards emerged. The only statistically significant excess mortality was for lung cancer (in women overall, and in persons living closest to the installations); this result is difficult to interpret in the absence of smoking data, and is not supported by other evidence but does not appear to be due to the social class distribution of the study group. The study did not support previously reported associations of exposure to electro-magnetic fields with acute myeloid leukaemia, other lymphatic cancers and suicide.
Int J Epidemiol. 1993 Feb;22(1):9-15.
Cancer mortality and residence near electricity transmission equipment: a retrospective cohort study.
Department of Epidemiology, University of Limburg, Maastricht, The Netherlands.
Several studies in recent years have raised the possibility that exposure to extreme low frequency (ELF) electromagnetic fields may be hazardous to human health, in particular by the promotion or initiation of leukaemia and other cancers. To determine if this exposure creates a long-term hazard to the public, the mortality of a group of people identified as having lived in an urban quarter of Maastricht in which two 150 kiloVolt (kV) powerlines and one transformer substation are located was investigated. Using the Dutch population registry it was possible to identify retrospectively 3549 inhabitants of the quarter who lived there for at least 5 years between 1956 and 1981. Of these 1552 study subjects lived within 100 m of the electricity transmission equipment and were exposed to magnetic field intensity of 1.0-11.0 milliGauss. The overall standardized mortality ratio and cancer mortality ratios were either not or only slightly elevated. The study does not support previously reported associations of exposure to ELF electromagnetic fields with leukaemia, brain cancer and breast cancer.
Am J Epidemiol. 2002 Mar 1;155(5):446-54.
Residential magnetic fields and the risk of breast cancer.
Program In Epidemiology, Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North MP-474, Seattle, WA 98109-1024, USA.
Chronic exposure to 60-Hz magnetic fields may increase the risk of breast cancer by suppressing the normal nocturnal production of melatonin. This population-based case-control study investigated whether such exposure is associated with an increased risk of breast cancer in women aged 20-74 years from the greater Seattle, Washington, area. Cases were diagnosed between November 1992 and March 1995 (n = 813); controls were identified by random digit dialing and were frequency matched by 5-year age groups (n = 793). Exposure was estimated using magnetic field measurements in the home at diagnosis, wiring configuration of all homes occupied in the 10 years prior to diagnosis, and self-reported measures of at-home electric appliance use. Odds ratios and 95% confidence intervals were estimated using conditional logistic regression with adjustment for other potential risk factors. Risk did not increase with measured nighttime bedroom magnetic field level, wiring configuration of the home at diagnosis, weighted summary wire codes of all homes occupied 5 and 10 years prior to diagnosis, or reported use of common household appliances, including bed-warming devices. These data do not support the hypothesis that exposure to residential magnetic fields is associated with an increased risk of developing breast cancer.
Am J Epidemiol. 2003 Nov 15;158(10):969-80.
Residential magnetic field exposure and breast cancer risk: a nested case-control study from a multiethnic cohort in Los Angeles County, California.
Epidemiology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA.
Some experimental and epidemiologic evidence suggests that residential exposure to power-frequency magnetic fields can increase breast cancer risk. This association was investigated in a nested case-control study of female breast cancer within a cohort of African Americans, Latinas, and Caucasians in Los Angeles County, California. Incident breast cancer was ascertained from 1993 to 1999 by linkage to county and state tumor registries. Controls were selected from a random sample of cohort members without breast cancer at baseline. Exposure was assessed in 1995-2001 by means of wiring configuration coding (an indirect measure of magnetic field exposure that has been associated with increased risk of childhood leukemia in Los Angeles and elsewhere in North America) in all homes occupied over the previous 10 years for 743 cases and 699 controls and by measurement of magnetic fields in the bedroom over a 7-day period for 347 cases and 286 controls. The estimated risk of breast cancer was not higher among women with wiring configuration codes associated with the highest magnetic fields (for a very high current configuration relative to very low, the adjusted odds ratio was 0.76 (95% confidence interval: 0.49, 1.18)). Stronger measured fields were not significantly associated with increased risk. These data suggest that residential magnetic field exposures commonly experienced by US women do not influence risk of breast cancer.
Am J Epidemiol. 2003 Jul 1;158(1):47-58.
Electromagnetic fields and breast cancer on Long Island: a case-control study.
Department of Preventive Medicine, School of Medicine, Stony Brook University, Stony Brook, NY 11794-8036, USA.
The EMF and Breast Cancer on Long Island Study (EBCLIS) was a case-control study designed to evaluate the possible association between exposure to electromagnetic fields (EMFs) and breast cancer. Eligible women were participants in the population-based Long Island Breast Cancer Study Project, were under 75 years of age at enrollment, were residentially stable, and were identified between August 1, 1996, and June 20, 1997. Of those eligible, 576 cases and 585 controls participated in EBCLIS (87% and 83%, respectively). In-home data collection included various spot and 24-hour EMF measurements, ground-current magnetic field measurements, wire mapping of overhead power lines servicing the home, and an interview. Odds ratios and 95% confidence intervals were based on multivariate logistic regression analyses. All odds ratios were close to 1 and nonsignificant. For the highest quartile of 24-hour EMF measurements, the odds ratio was 0.97 (95% confidence interval (CI): 0.69, 1.37) in the bedroom and 1.09 (95% CI: 0.78, 1.51) in the most lived-in room. For the highest exposure category of ground-current measurements, the odds ratio was 1.13 (95% CI: 0.88, 1.44) in the bedroom and 1.08 (95% CI: 0.85, 1.38) in the most lived-in room. These and other EBCLIS results agree with other recent reports of no association between breast cancer and residential EMF exposures.
Am J Epidemiol. 2004 May 1;159(9):852-61.
Residential and occupational exposures to 50-Hz magnetic fields and breast cancer in women: a population-based study.
The Cancer Registry of Norway, Institute of Population-based Cancer Research, Oslo, Norway.
A case-control study was conducted to investigate whether residential and occupational exposures to magnetic fields increased the risk for breast cancer among women. Cases of breast cancer diagnosed during 1980-1996 were identified in a cohort of women living near a high-voltage power line in Norway in 1980 or between 1986 and 1996. Each case was matched by year of birth, municipality, and first year of entry into the cohort with two randomly selected controls without cancer. Residential exposure to magnetic fields was calculated as that generated by the lines before diagnosis, and occupational exposure was based on exposure matrix data. Women with residential exposure had an odds ratio of 1.58 (95% confidence interval (CI): 1.30, 1.92) when compared with unexposed women. The odds ratios for exposed women versus unexposed women with estrogen receptor (ER)-positive and ER-negative breast cancer were 1.33 (95% CI: 0.93, 1.90) and 1.40 (95% CI: 0.78, 2.50), respectively (ER status was available for 44% of the cases). Women with the highest occupational exposure had an odds ratio of 1.13 (95% CI: 0.91, 1.40) when compared with those unexposed at work. The findings suggest an association between exposure to magnetic fields and breast cancer in women.
The studies included here are the ones cited by major review groups and may not be completely comprehensive.
Studies of occupational exposure
Br J Ind Med. 1993 Aug;50(8):758-64.
Incidence of cancer in persons with occupational exposure to electromagnetic fields in Denmark.
INSERM U88, Paris, France.
Several studies suggest that work in electrical occupations is associated with an increased risk of cancer, mainly leukaemia and brain tumours. These studies may, however, not be representative if there is a publication bias where mainly positive results are reported. To study an unselected population the incidence of cancer was followed up over a 17 year period (1970-87) in a cohort of 2.8 million Danes aged 20-64 years in 1970. Each person was classified by his or her industry and occupation in 1970. Before tabulation of the data on incidence of cancer, each industry-occupation group was coded for potential exposure to magnetic fields above the threshold 0.3 microT. Some 154,000 men were considered intermittently exposed and 18,000 continuously exposed. The numbers for women were 79,000 and 4000 respectively. Intermittent exposure was not associated with an increased risk of leukaemia, brain tumours, or melanoma. Men with continuous exposure, however, had an excess risk of leukaemia (observed (obs) 39, expected (exp) 23.80, obs/exp 1.64, 95% CI 1.20-2.24) with equal contributions from acute and other leukaemias. These men had no excess risk of brain tumours or melanoma. A risk for breast cancer was suggested in exposed men but not in women. The risk for leukaemia in continuously exposed men was mainly in electricians in installation works and iron foundry workers. Besides electromagnetic fields other exposures should be considered as possible aetiological agents.
Am J Ind Med. 1997 May;31(5):534-44.
Mortality among a cohort of electric utility workers, 1960-1991.
EcoAnalysis, Inc., Ojai, CA, USA.
Overall mortality trends among an electric utility workforce are examined. The study cohort (n = 40,335) included all workers with at least 1 year of work experience from 1960-1991; 3,753 deaths were observed in this cohort. Standardized mortality ratios (SMRs) and internal cohort analyses were used to assess mortality trends for the entire cohort and for specific occupational groups. Most SMRs were < or = 1.0 and were generally lower for noncancer (cardiovascular, COPD, and injuries) than for cancer mortality. Compared to office staff, rate ratios (RR) were higher for respiratory cancers for field staff [(RR = 2.3, 95% CI, 1.0-5.0) linecrew (RR = 2.2 95% CI, 1.5-3.1), and power plant occupations (RR = 2.4, 95% CI, 1.6-3.6)]. Nonmanagement occupations had rate ratios for motor vehicle injuries and all types of injuries, within a range of 2.5-4.7, with all lower CIs > 1.0. The healthy worker effect is an important factor in explaining the difference between SMR and internal cohort analyses results. The SMR results indicate that this workforce has lower rates for overall mortality, cardiovascular disease, cancer and nonintentional injury. A consistent finding in the internal cohort analyses that merits further research was higher mortality rates for respiratory cancer and injuries among nonoffice staff.
Br J Ind Med. 1985 Mar;42(3):191-5.
Cancer morbidity among workers in the telecommunications industry.
A retrospective cohort study of 2918 workers in the telecommunications industry in Sweden recorded the cancer morbidity for the period 1958-79. Cases of cancer were collected from the Swedish Cancer Registry for this period and information on work characteristics was collected for the entire period of employment. The total cancer morbidity was as expected. There was no excess risk of lung cancer but an excess risk of malignant melanoma of the skin was detected (SMR = 2.6, 12 cases). This excess risk was particularly associated with work environments where soldering was practised. Estimates of the SMR became larger with the assumption of a longer induction/latency period.
Br J Ind Med. 1983 May;40(2):188-92.
Incidence of cancer in the electronics industry: using the new Swedish Cancer Environment Registry as a screening instrument.
The object of this study was to assess the relative risks of cancer for a particular branch of industry by using the newly created cancer environment registry. The registry was created by a record linkage of the 1960 census to the Swedish Cancer Registry 1961-73. A cohort study was undertaken of all subjects classified in the census as working in the electronics or electrical manufacturing industry. The risks were calculated in relation to the general working population. The results showed a slightly higher total incidence of cancer (all sites) in this branch of industry than in the general working population, for men as well as for women. This was especially so for tumour sites connected with the pharynx and the respiratory system. The study also indicates that the new registry has a potential as a screening instrument.
Environ Health Perspect. 1999 Feb;107 Suppl 1:145-54.
Industrialization, electromagnetic fields, and breast cancer risk.
Environment Group, Electric Power Research Institute, Palo Alto, CA 94303, USA.
The disparity between the rates of breast cancer in industrialized and less-industrialized regions has led to many hypotheses, including the theory that exposure to light-at-night and/or electromagnetic fields (EMF) may suppress melatonin and that reduced melatonin may increase the risk of breast cancer. In this comprehensive review we consider strengths and weaknesses of more than 35 residential and occupational epidemiologic studies that investigated the association between EMF and breast cancer. Although most of the epidemiologic data do not provide strong support for an association between EMF and breast cancer, because of the limited statistical power as well as the possibility of misclassification and bias present in much of the existing data, it is not possible to rule out a relationship between EMF and breast cancer. We make several specific recommendations for future studies carefully designed to test the melatonin-breast cancer and EMF-breast cancer hypotheses. Future study designs should have sufficient statistical power to detect small to moderate associations; include comprehensive exposure assessments that estimate residential and occupational exposures, including shift work; focus on a relevant time period; control for known breast cancer risks; and pay careful attention to menopausal and estrogen receptor status.
J Natl Cancer Inst. 1994 Jun 15;86(12):921-5.
Breast cancer mortality among female electrical workers in the United States.
Department of Epidemiology, University of North Carolina School of Public Health, Chapel Hill 27599-7400.
BACKGROUND: Previous epidemiologic studies have suggested that exposure to electric or magnetic fields in occupational and residential environments may cause cancer. Recent experimental findings provide some support for the hypothesis that exposure to extremely low-frequency electromagnetic fields reduces the pineal gland's nocturnal production of the hormone melatonin, thereby increasing susceptibility to sex hormone-related cancers such as breast cancer.
PURPOSE: Our purpose was to assess the evidence that cancer of the female breast might be associated with exposure to extremely low-frequency electromagnetic fields.
METHODS: Records of women who had breast cancer as the underlying cause of their death (ICD-9 174) and control subjects (four per case) were selected from computer files of U.S. mortality data for the years 1985-1989. Women 20 years and older at the time of their death were eligible for inclusion if they were residents of and died in one of the 24 states that provided death certification records with occupation and industry codes to the National Center for Health Statistics for at least 1 year during the study interval. Data from death certificates were used to classify the case and control subjects with regard to potential occupational exposure to electric and magnetic fields. Control subjects were a random sample of women who died of any other underlying cause, excluding leukemia and brain cancer.
RESULTS: The data analysis contrasted 68 women with breast cancer and 199 controls, all with electrical occupations, with 27,814 women with breast cancer and 110,750 controls, all of whom had other occupations. Electrical workers had excess mortality from breast cancer relative to other employed women [odds ratio (OR) = 1.38; 95% confidence interval (CI) = 1.04-1.82]). Adjusted ORs for specific electrical occupations were 1.73 (95% CI = 0.92-3.25) for electrical engineers, 1.28 (95% CI = 0.79-2.07) for electrical technicians, and 2.17 (95% CI = 1.17-4.02) for telephone installers, repairers, and line workers. There was no excess of breast cancer, however, in seven other occupations held more frequently by women and also involving potentially elevated electrical exposures, including telephone operators, data keyers, and computer operators and programmers.
CONCLUSIONS: In light of the limitations inherent in death certification data and the design of this study, any conclusions regarding the hypothesis that exposure to extremely low-frequency electromagnetic fields causes breast cancer among women must be limited. Nevertheless, our findings are broadly consistent with that hypothesis and encourage further investigation with improvements in study design and data quality.
Am J Epidemiol. 2005 Feb 1;161(3):250-9.
Occupational magnetic fields and female breast cancer: a case-control study using Swedish population registers and new exposure data.
Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
Several recent epidemiologic studies on occupational magnetic field exposure have suggested an association with female breast cancer. The purpose of this study was to test this hypothesis by using the extensive Swedish population registers in combination with improved exposure assessment. The study base consisted of all women between 1976 and 1999 gainfully employed in Stockholm or Gotland County in Sweden. A total of 20,400 cases of breast cancer were identified from the cancer registry, and 116,227 controls were selected randomly from the study base. Information was available on estrogen receptor status, occupation, socioeconomic status, and age. Parity was available for a subset. The exposure was assessed by linkage to a newly developed job-exposure matrix based on personal magnetic field measurements on women. All risk estimates were close to unity regardless of exposure cutpoint or choice of exposure parameter. The overall odds ratio for women exposed to 0.30 microT or more was 1.01 (95% confidence interval: 0.93, 1.10). The size of the study allowed for estimates with good precision also in subgroups where previous studies have suggested increased risk, but the findings do not support the hypothesis that magnetic fields influence the risk of female breast cancer.
These studies were taken from those listed by major review groups and may not be completely comprehensive