In June 2003, scientists reported findings from a population-based study to evaluate whether exposure to electromagnetic fields (EMFs) is associated with increased risk for breast cancer in Long Island (Nassau and Suffolk counties), N.Y. They did not find an association between exposure to EMFs and increased risk for breast cancer. This study, titled "Electromagnetic Fields and Breast Cancer on Long Island: A Case-Control Study,"* is part of the Long Island Breast Cancer Study Project (LIBCSP).
1. What is the Electromagnetic Fields and Breast Cancer on Long Island Study?
The Electromagnetic Fields and Breast Cancer on Long Island Study is a population-based case-control study conducted to evaluate whether electromagnetic fields (EMFs) are associated with increased risk for breast cancer among women in Nassau and Suffolk counties, N.Y. The study consisted of 576 women (cases) who were newly diagnosed with breast cancer between August 1, 1996, and June 20, 1997, and 585 women (controls) who did not have the disease. All of the women were under 75 years of age and had resided in their current homes in Nassau and Suffolk counties for at least 15 years before the time of diagnosis of breast cancer (cases), or at the time they were identified (controls) for the study. The study included a comprehensive in-home assessment of exposure to EMFs. The research was conducted by M. Cristina Leske, M.D., M.P.H., of Stony Brook University, N.Y., and colleagues.
The study population was drawn from the larger study population of the Breast Cancer and Environment on Long Island Study. Women in the larger study were invited to participate in the EMF study if they had lived in their homes for at least 15 years and were under 75 years of age. (The number of women age 75 and older who were eligible to participate in the study was too small to include.) Both studies are part of the Long Island Breast Cancer Study Project (LIBCSP).
2. What is the Long Island Breast Cancer Study Project (LIBCSP)?
The Long Island Breast Cancer Study Project (LIBCSP) is an investigation of possible environmental causes of breast cancer in Suffolk, Nassau, and Schoharie counties, New York, and Tolland County, Conn. It is sponsored and funded by the National Cancer Institute (NCI) and the National Institute of Environmental Health Sciences (NIEHS). The project consists of more than 10 studies that include human population (epidemiologic) studies, a family breast and ovarian cancer registry, and laboratory research designed to help explain the development of breast cancer. Additional analyses from some of the research are still ongoing, but findings have been reported from all but two of the studies, the Breast Cancer and Environment on Long Island Follow-up Study and the Environmental Exposures and Breast Cancer on Long Island Study. The project also includes the development of a research tool, a Geographic Information System (GIS-H) for Breast Cancer Studies on Long Island, which allows scientists to explore new hypotheses on environmental risk factors for breast cancer.
3. What are electromagnetic fields (EMFs)?
EMFs are invisible areas of energy that result from the flow of electric current. Common sources of EMFs include power lines, electrical wiring, and appliances. While electric and magnetic fields are related, they have different properties. The strength of both electric and magnetic fields decreases rapidly with increased distance from the source. Because magnetic fields are not easily shielded by most objects, as electric fields are, it is generally believed that any possible health effects of EMFs would be due to magnetic fields, not electric fields.
Residential magnetic fields, such as those investigated in the study, are in the extremely low frequency (ELF) range of the electromagnetic spectrum. The ELF range includes frequencies (measured in Hertz or cycles per second) between 3 and 3000 Hertz. The strength (magnitude) of magnetic fields is measured in gauss (G) or tesla (T): 1 milligauss (mG) = 0.1 microtesla (mT); milli (m) = 1 thousandth; and micro(m) = 1 millionth.
4. Why were EMFs studied?
Scientists hypothesized that exposure to extremely low frequency magnetic fields may increase breast cancer risk by affecting melatonin production. Melatonin is a hormone produced in response to a lack of light by the pineal gland, which is located at the base of the brain. Melatonin levels are typically low during the day, and increase at night, peaking between 2 and 4 a.m. Exposure to light-at-night (for example, as in shift work) or exposure to higher levels of magnetic fields are thought to suppress this normal nocturnal rise in melatonin. Melatonin levels are believed to be inversely related to estrogen levels, in that when melatonin levels are low, estrogen levels are high and vice versa. Therefore, if light-at-night or magnetic field levels suppress the normal nocturnal rise in melatonin, estrogen levels would subsequently be increased. Since increased levels of estrogen are hypothesized to increase the risk of breast cancer, this suppression of melatonin by either light-at-night or magnetic fields could possibly increase the risk of breast cancer.
Previous studies have shown inconsistent results linking residential and/or occupational EMF exposure and breast cancer in women. Most studies did not include direct EMF measurements at home or in the workplace. The first study to measure EMFs directly in homes was conducted by scientists at Fred Hutchinson Cancer Research Center, Seattle, Wash., and found no association between residential EMF exposure and breast cancer.
5. How was this Long Island study conducted?
The scientists conducted a comprehensive home assessment of the study participants' exposure to EMFs through personal interviews and by taking a variety of EMF measurements within and around the outside of the home. The measurement methods were based upon the results of a pilot study which is described in another scientific paper. EMFs were measured in the following ways:
-24-hour measurements were taken in the bedroom and the most frequently used room aside from the bedroom and kitchen (most lived-in room)
-Spot measurements were taken at the front door, bedroom, and the most lived-in room
-Ground-current magnetic field measurements, which are electrical currents that are sometimes present in a home's electrical grounding system (usually the plumbing), were taken at the center of the bedroom and the most lived-in room
-Wire coding (or wire mapping) in which the type of wiring surrounding a home and the distance from this wiring was recorded and coded using the Wertheimer-Leeper and Kaune-Savitz systems.
The 24-hour, spot, and ground-current measurements were taken with specially designed equipment to measure EMFs. A questionnaire was used to gather data on residential history, housing construction history, occupational exposures, electric appliance use, and exposure to light-at-night and shift work.
6. What were the findings?
The scientists found no association between residential exposure to EMFs and breast cancer. Levels of in-home spot, 24-hour, ground-current measurements, and wire codes did not differ between women who were diagnosed with breast cancer (cases) and women who did not have the disease (controls). Further, differences in risk were not observed between the two groups when the data were analyzed controlling for age, family history of breast cancer, personal history of benign (non-cancerous) breast disease, number of children (parity), and education. The findings are reported by the research team in the July 1 issue of the American Journal of Epidemiology. The authors are Dr. Leske, Elinor R. Schoenfeld, Ph.D., Erin S. O'Leary, Ph.D., Kevin Henderson, B.S., Roger Grimson, Ph.D., Geoffrey C. Kabat, Ph.D., and Sang Ahnn, Ph.D., Stony Brook University; William T. Kaune, Ph.D., EM Factors, Richland, Wash.; and Marilie D. Gammon, Ph.D., University of North Carolina at Chapel Hill.
7. What is the significance of the study?
These findings are similar to those reported last year by scientists at Fred Hutchinson Cancer Research Center. Both of these studies included a comprehensive set of in-home measurement of EMF exposure and wire codes. This new study led by Stony Brook University scientists included ground-current magnetic field measurements, which were not included in the earlier study. In addition, the study included only long-term residents, with the objective of assessing exposures over an extended time period.
The EMF and Breast Cancer on Long Island Study had a large sample size and high participation rates. It used the best available methods to estimate past exposure to magnetic fields in the home. Because study participants lived in their homes for 15 years or more, the in-home measurements are likely to be indicators of their past exposures. Multiple methods were used to assess in-home exposure, using various techniques and approaches. Further, the study followed a standardized protocol with many quality control procedures.
8. Are the scientists conducting further research?
A scientific paper describing the wire coding methods will be published in the July 15 issue of the International Journal of Exposure Analysis and Environmental Epidemiology. A paper presenting study results on the use of electric blankets in cases and controls published in the September 1, 2003, issue of Epidemiology . The scientists are analyzing data on use of electrical appliances, shift work and light-at-night, and occupational exposure.
9. Why was the LIBCSP conducted?
There has been a pattern of elevated mortality rates (the number of deaths per year) for female breast cancer extending from the Mid-Atlantic through the Northeastern states that has persisted for many years. Established risk factors are believed to be largely responsible, such as increasing age and having a family history of breast cancer, but the remaining reasons are unknown. Incidence rates (the number of breast cancer cases newly diagnosed each year) in Nassau, Suffolk, and Schoharie counties, N.Y., and in Tolland County, Conn., were above the United States average at the time the LIBCSP began. For this reason, the project and other studies have been undertaken to try to learn if there are environmental exposures that may be responsible.
Public Law 103-43, enacted in 1993, directed that NCI conduct a study of "potential environmental and other risks contributing to the incidence of breast cancer" in Nassau, Suffolk and Schoharie counties, N.Y., and Tolland County, Conn. The law also stated that the study on Long Island "should include the use of a geographic system to evaluate the current and past exposure of individuals, including direct monitoring and cumulative estimates of exposure to contaminated drinking water; sources of indoor and ambient air pollution, including emissions from aircraft; electromagnetic fields; pesticides and other toxic chemicals; hazardous and municipal waste; and such other factors as the director [of NCI] determines to be appropriate."
10. What other research has been conducted as part of the LIBCSP?
Breast Cancer and the Environment on Long Island Study. This population-based case-control study was conducted to determine if polycyclic aromatic hydrocarbons (PAH), a pollutant caused by incomplete combustion of various chemicals including diesel fuel and cigarette smoke, and organochlorine compounds, chemicals found in many pesticides, are associated with increased risk for breast cancer among women on Long Island. The scientists found that organochlorine compounds are not associated with increased risk for breast cancer on Long Island. Exposure to PAHs was associated with a modest increased risk for breast cancer. This finding is consistent with a few, much smaller epidemiologic studies and suggests the need for additional research in other populations. The research also confirmed the presence of many of the well-known breast cancer risk factors among the study population. These risk factors included increasing age, having a family history of breast cancer, having a first child at a later age, never having given birth to a child, and having higher income. The findings were reported in 2002 and are described in an NCI Q&A (August 6, 2002) at http://www.cancer.gov/newscenter/LIBCSPqanda. The principal investigator is Marilie D. Gammon, Ph.D., University of North Carolina at Chapel Hill.
Breast Cancer and the Environment on Long Island Follow-Up Study. Women who were diagnosed with breast cancer and who participated in the Breast Cancer and the Environment on Long Island Study (described above) continue to be followed to determine whether organochlorine compounds, PAHs, and lifestyle factors influence survival. Findings are expected about 2006. Dr. Gammon is the principal investigator.
Epidemiology of Breast Cancer on Long Island. This hospital-based case-control study investigated breast cancer risk in relation to levels of organochlorine pesticide compounds in Nassau and Suffolk counties (Long Island) and Schoharie County, N.Y. The scientists found that increased risk for breast cancer did not appear to be associated with past exposure to organochlorine compounds. There was no association between breast cancer risk and levels of total pesticides or total polychlorinated biphenyls (PCBs). PCBs are a group of chemical compounds found in coolants and lubricants in transformers, capacitors, other electrical equipment, and some consumer products. The principal investigator is Steven D. Stellman, Ph.D., American Health Foundation, Valhalla, N.Y., now at Columbia University, New York.
Organochlorines and Risk of Breast Cancer. This pilot hospital-based case-control study investigated the relationship between exposure to organochlorine compounds and risk for breast cancer in Tolland County, Conn. Data on the Tolland County study population were included in a larger hospital-based case-control study of women from Connecticut that did not find an association between organochlorine compounds and increased risk for breast cancer. The principal investigator is Tongzhang Zheng, M.D., Sc.D., Yale University, New Haven, Conn.
Reducing Barriers to Use of Breast Cancer Screening. This study investigated whether a telephone counseling intervention aimed at women who are known to underuse breast cancer screening can, with or without an accompanying educational intervention for their physicians, increase use of breast cancer screening. Women who had a previous mammogram at the start of the study and who subsequently received telephone counseling were more likely to become regular mammography users than women who did not receive counseling. In addition, the findings suggested that the educational intervention for physicians is associated with initiation of mammography use among women who have never had a mammogram. More research with larger samples is needed to confirm this finding. The principal investigator is Dorothy S. Lane, M.D., Ph.D., Stony Brook University.
Metropolitan New York Registry of Breast Cancer Families. The registry is recruiting families who have a history of breast and/or ovarian cancer. Participants are asked to contribute information, blood, and urine samples that can be used for studies on the causes of these diseases. The registry is one of six international registry sites funded by NCI to provide scientists a source of information and specimens to speed their investigations into the causes of breast cancer. Rubie Senie, Ph.D., Columbia University, is the principal investigator. Families who are interested in participating in the registry may call Columbia University at 1-888-METRO-08 (1-888-638-7608).
Environmental Exposures and Breast Cancer on Long Island. This investigation is being conducted to determine whether length of residence in close proximity to hazardous waste sites, industrial sites, or toxic release inventory sites; prior land use (for example, farm land); and exposure to various chemicals in drinking water may increase risk for breast cancer on Long Island. Findings are expected to be reported in late 2003. The principal investigator is Erin O'Leary, Ph.D., Stony Brook University.
Estrogen Metabolites as Biomarkers for Breast Cancer Risk. In this study, investigators examined whether differences in the way women's bodies process the natural hormone estrogen may be related to breast cancer risk. Estrogen is metabolized by two main, competing pathways, either to 2-hydroxyestrone or to 16-alpha-hydroxyestrone. Some research has suggested that the balance between the estrogen metabolite 16-alpha-hydroxyestrone, which has been associated with breast cancer, and 2-hydroxyestrone, which has not, may affect risk for the disease. The scientists found that postmenopausal women with very low levels of the "good" metabolite (2-hydroxyestrone) relative to the "bad" metabolite (16-alpha-hydroxyestrone) had a greatly increased risk of breast cancer, compared to women with high levels of the "good" metabolite. Because of the small number of study participants, further study is needed to confirm the findings. The principal investigator is H. Leon Bradlow, Ph.D., Strang Cancer Prevention Laboratory, New York.
Regulation of Scatter Factor Expression in Breast Cancer. This research evaluated how a growth factor called scatter factor may regulate growth of breast cancer. Using tissue samples from Long Island women, the scientists found that levels of scatter factor are higher in invasive breast cancers than in non-invasive cancers. It also causes human breast cancer cells to move faster and to be more invasive in cell cultures. Further, the growth factor induces breast cells to produce an enzyme that degrades tissue, thus facilitating tumor invasion, and stimulates formation of new blood vessels, which is essential for tumor growth and spread. The principal investigator is Eliot M. Rosen, M.D., Ph.D., Long Island Jewish Medical Center, New Hyde Park, N.Y.
RDA Analysis of Breast Cancer . The study examined genetic changes in breast tumor tissue from patients on Long Island using a technique called representational difference analysis (RDA). Certain alterations in genes may be linked to environmental exposures, and certain mutations may be characteristic of specific exposures. The principal investigator is Michael H. Wigler, Ph.D., Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.
11. What is the Geographic Information System (GIS-H) for Breast Cancer Studies on Long Island?
NCI has developed a prototype health-related geographic information system (GIS-H) for Long Island as part of the LIBCSP. This advanced research tool provides scientists a mechanism to investigate relationships between breast cancer and the environment on Long Island. It also enables scientists to estimate exposure to environmental contamination.
GISs are powerful computer systems that permit layers of information to be superimposed and manipulated. The systems consist of hardware, software, and data tables. The "H" in GIS-H stands for "health," because the system potentially can be used for research on other types of cancer, and other diseases and conditions.
The GIS-H consists of more than 80 databases that have geographic, demographic, health, and environmental data on Nassau and Suffolk counties and, to a lesser extent, on surrounding counties. It also has statistical and analytical tools for scientists.
The GIS-H also will provide an internet mapping facility for the public. Visitors will be able to see and use some of the content and features of the GIS-H without needing special computer skills. They may choose from a list of interactive maps available on the Web site or choose to install the ArcExplorer mapping software on their computers. This software allows visitors to access GIS-H map services to construct their own maps.
*Schoenfeld, ER, et al. Electromagnetic Fields and Breast Cancer on Long Island: A Case-Control Study. American Journal of Epidemiology 158:47-58, 2003.
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Tuesday, June 24, 2003
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