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Among more recent studies, findings have been mixed. Some have found an association; others have not. These studies are discussed in the following paragraphs. Currently, researchers conclude that there is limited evade ce that magnetic fields from power lines cause childhood leukemia, and that there is inadequate evide ce that these magnetic fields cause other cancers in children (2). Researchers have not found a consis ent relationship between magnetic fields from power lines or appliances and childhood brain tumors. In one large study by the National Cancer Institute (NCI) and the Children's Oncology Group, researchers meas red magnetic fields directly In homes (4). This study found that children living in homes with high magn tic field levels did not have an increased risk of childhood acute lymphobiastic leukemia. The one excep ion may have been children living in homes that had fields greater than 0.4 microtesla (pT), a very high level t at occurs in few residences. Another study conducted by NCI researchers reported that children living close to overhead power lines based on distance measurements were not at greater risk of leukemia (5). To est mate more accurately the risks of leukemia in children from magnetic fields resulting from power lines, resear hers pooled (combined) data from many studies. In one pooled study that combined nine well-conducted studies from several countries, including a study from the NCI, a twofold excess risk of childhi iod leukemia was associated with exposure to magnetic fields above 0.4 pT (6). In another pooled study hat combined 15 studies, a similar increased risk was seen above 0.3 pT (7). It is difficult to determine if this evel of risk represents a real increase or if it results from study bias. Such study bias can be related to the se ection of study subjects or possibly to other factors that relate to levels of magnetic field exposure. If magnetic fields caused childhood leukemia, certain patterns would have been found such as increasing risk with ir creasing levels of magnetic field exposure. Anoth r way that people can be exposed to magnetic fields is from household electrical appliances. Several studie have investigated this relationship (2). Although magnetic fields near many electrical appliances are higher than near power lines, appliances contribute less to a person's total exposure to magnetic fields. This is because most appliances are used only for short periods of time, and most are not used close to the body, whereas power lines are always emitting magnetic fields. In a detailed evaluation, investigators from NCI and the Children's Oncology Group examined whether the use of household electrical appliances by the mother while pregnant and later by the child increased the risk of childh od leukemia. Although some appliances were associated with childhood leukemia, researchers did not find ar y consistent pattern of increasing risk with increasing years of use or how often the appliance was used (8). A few other studies have reported mostly inconsistencies or no relation between appliances and risk of childh od cancer. Occupational exposure of mothers to high levels of magnetic fields during pregnancy has been associated with childhc od leukemia in a Canadian study (9). Similar studies need to be done in other populations to see if this is indeed the case. 3. Is these a link between magnetic field exposure in the home and cancer in adults? Althou h several studies have looked into the relationship of leukemia, brain tumors, and breast cancer in adults xposed to magnetic fields in the home, there are only a few large studies with long -term, magnetic field m asurements. No consistent association between magnetic fields and leukemia or brain tumors has been a tablished. The majority of epidemiological studies have shown no relationship between breast cancer in women and magnetic fields from electrical appliances. Recent studies of breast cancer and magnetic fields in the home have included direct and indirect magnetic field measurements. These studies mostly found no association betweE n breast cancer in females and magnetic fields from power lines or electric blankets (10, 11, 12, 13), A Norm egian study found a risk for exposure to magnetic fields in the home (14), and a study in Africa - American women found that use of electric bedding devices may increase breast cancer risk (15). 4. Is these a link between magnetic field exposure at work and cancer in adults? Several studies conducted in the 1980s and early 1990s reported that people who worked in some electrical occupations (such as power station operators and phone line workers) had higher than expected rates of some types of cancer, particularly leukemia, brain tumors, and male breast cancer (2). Some occupational studies showed very small increases in risk for leukemia and brain cancer, but these results were based on job titles and not actual measurements. More recently conducted studies that have included both job titles and 3.46 4/21/05 Page 2