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Environment more important than heredity to cancer risk, study suggests


July 13, 2000
Web posted at: 12:32 p.m. EDT (1632 GMT)

ATLANTA (CNN) -- Environmental factors and lifestyle choices may play a greater role in cancer development than genetic factors, a European study suggests.

Their work is published in this week's New England Journal of Medicine.

The researchers studied 44,788 pairs of twins from Denmark, Sweden and Finland. They used twins because identical twins share 100 percent of their genetic material and fraternal twins share at least 50 percent. If one twin developed cancer and the other didn't, that helped the researchers conclude that the disease is not strictly hereditary.

Researchers concluded that "inherited genetic factors make a minor contribution to susceptibility to most types" of cancer. Instead, environmental factors seemed more important.

Those factors "encompass everything that is not genetic," said Heather Spencer Feigelson, Ph.D., a genetic epidemiologist with the American Cancer Society, "including important lifestyle behaviors such as tobacco use, diet and exercise habits, reproductive characteristics, infectious agents and medication use. Thus, it is a much broader context than the idea of environmental factors being limited to substances such as pesticides, air pollutants or toxic waste." Fiegelson was not involved in the study.

In an editorial accompanying the Scandinavian study, Dr. Robert N. Hoover of the National Cancer Institute in Rockville, Maryland, said the work should easily dispel a common misconception -- "the fatalism of the general public about the inevitability of genetic effects."

Fiegelson agreed. Many people think "if you have a family history you are sort of doomed," she said. "That is not the case."

In fact, the researchers identified only a few cancers that seemed to have a significant genetic influence, including breast cancer, colorectal cancer and prostate cancer. But even among these groups, they said, the risk of both twins developing the disease was moderate.

The researchers did not look at the genetic makeup of each twin, so they were not able to evaluate how much a person's genes contributed to cancer if the environmental triggers existed. If environmental factors in Scandinavia are different from those in other places, they wrote, the proportion of cancer risk due to heredity may also differ.

The researchers also did not study the potential effect of precautionary measures. For instance, if one twin was diagnosed with cancer, the other may have been screened and a precancerous lesion caught early.

The study results indicate more needs to be learned about the role of both genes and environment, experts said. "You can't simplify it by saying it is all nature or it is all nurture, because it is both," Fiegelson said.

In his supporting editorial in the medical journal, Hoover agreed, saying scientists should take every opportunity to study all possible causes of cancer, whether genetic or not.

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The New England Journal of Medicine
American Cancer Society

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