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- BOSTON (Reuters) - Scandinavian
researchers found that the main causes of cancer are the substances to
which people are exposed, not their genes, according to a report in New
England Journal of Medicine.
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- The scientists from Sweden, Denmark and Finland studied
nearly 90,000 pairs of twins and found that heredity accounted for 42 percent
of prostate cancers, 35 percent of colorectal cancers, and 27 percent of
breast tumours.
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- The figures show most people are not destined to develop
cancer because of their genetic makeup, Dr. Robert N. Hoover of the U.S.
National Cancer Institute in Rockville, Maryland, wrote in a Journal editorial
about the study.
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- But the scientists, led by Paul Lichtenstein of the Karolinska
Institute in Stockholm, also concluded that the sizeable role that heredity
plays in the development of some types of tumours "suggests major
gaps in our knowledge of the genetics of cancer."
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- In the past, doctors suspected that 80 to 90 percent
of cancers were caused by environmental factors such as tobacco, alcohol,
radiation, infections, pollutants, workplace chemicals, diet and drugs,
according to the Journal citing National Cancer Institute data.
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- The Scandinavian work, "provides new and valuable
information for the nature- versus-nurture debate," Hoover said.
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- To develop the estimates, Lichtenstein and his colleagues
relied on the premise that inherited tumours are more likely to appear
in both identical twins because they share the same genetic makeup.
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- Cancers caused by the environment are more likely to
be shared by non- identical twins, who typically have 50 percent of their
genetic material in common.
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- The researchers gathered twin and cancer data from Swedish
and Danish twin registries, along with Finland's Central Population Register,
producing a database four times larger than any previous study, Hoover
said.
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- In general, the Lichtenstein team found twins share a
similar cancer risk, whether or not they are identical.
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- "This was especially evident for cancer of the stomach,
colourectum, lung, breast and prostate," they said.
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- Although the Lichtenstein team found that heredity played
no role in cancers of the cervix or uterus, it accounted for 22 percent
of the ovarian and 27 percent of the breast cancers.
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- In other categories for both men and women, heredity
was found to be the source of 36 percent of pancreatic cancers, 31 percent
of bladder cancers, 28 percent of stomach tumours, 26 percent of lung cancers,
and 21 percent of leukaemias.
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