A New View of ELF-EMFs.

Are They Linked with Cancer Promotion?

The debate over a possible link between cancer and extremely low frequency electromagnetic fields (ELF-EMFs) began with a 1979 study that found excess cancer in people who lived near large electrical wires. It has continued through subsequent in vitro, in vivo, and epidemiological studies that often produced conflicting results. In this issue, Gang Chen of the Department of Pediatrics and Human Development at Michigan State University and colleagues used an experimental model developed to test cancer-promoting chemicals to examine whether ELF-EMFs might play a role in cancer promotion [EHP 108:967-972].

The development of cancer is a multistage process. During normal development, immature cells undergo a process called differentiation in which they become highly specialized (developing, for instance, into red blood cells) and are less able to continue proliferating. In the first stage of cancer, initiation, a cell's DNA is damaged through mutation, causing a differentiated cell to resemble an immature one, in effect reversing the process of differentiation. In the second stage, promotion, normal cellular controls go awry, and the mutated cell multiplies. ELF-EMFs are too weak to kill cells or (most scientists agree) to cause mutations and thus initiate cancer. However, they could play a role during the promotion stage of cancer, which involves so-called epigenetic mechanisms (those that affect gene expression rather than gene structure) and induce cancer in cells that have already mutated.

In the laboratory, differentiation--which can be stimulated by chemical treatment--can transform initiated cells into mature cells, converting cells that had started to become cancerous into normal-seeming adult cells. In this case, differentiation seems to be a healing process that nullifies the mutation. What the group was testing was whether ELF-EMFs could prevent differentiation in cells that had started down the road to cancer.

The research used mouse leukemia cells that, when treated with dimethyl sulfoxide (DMSO), differentiate into red blood cells. The researchers group compared control cells, cells treated with DMSO, and cells treated with DMSO and maintained inside a culture chamber exposed to a 60-hertz ELF-EMF at varying strengths. In a system used to investigate the epigenetics of cancer promotion, the scientists measured three end points. Proliferation, or cell growth, was determined by measuring DNA concentration. Differentiation was measured by detecting hemoglobin, a sign that the cell had developed into a red blood cell. Youthfulness was gauged by measuring telomerase, the enzyme that builds telomeres, which keep chromosomes "young" and able to divide.

Starting at a threshold dose of about 20 milligauss (a measure of the strength of the electrical field), the 60-hertz ELF-EMF caused a dose-dependent reduction of differentiation, as well as an increase in telomerase and proliferation. These effects resemble those of chemical cancer promoters. (Under a power line, fields measure roughly 300 milligauss, and near home appliances they can exceed 1 gauss.)

While the study showed that ELF-EMFs could conceivably play a biological role in carcinogenesis, cancer-promoting chemicals require a long exposure to promote cancer, and human exposures to ELF-EMFs are hard to gauge. Because electric fields change so radically from point to point, it's too early to say if typical exposures actually promote cancer. But by stressing the importance of promotion, the study could focus future research on the environmental health effects of ELF-EMFs.