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- WASHINGTON - A monkey virus
once found in millions of doses of polio vaccines and now suspected of
causing cancer may work by rearranging a victim's DNA, researchers said
on Wednesday.
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- They said the theory that viruses can cut up and reshuffle
DNA could explain suggestions =97 which are hotly debated =97 that polio
vaccin= es contaminated with a monkey virus in the 1950s and 1960s might
cause cancer.
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- Dr. Brian Durie of Cedars-Sinai Hospital in Los Angeles
and Dr. Howard Urnovitz of the Chronic Illness Research Foundation in Berkeley,
Calif., said their idea offered a mechanism for how the virus might cause
cancer.
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- Some polio vaccines are grown using kidney tissue from
monkeys. Between 1955 and 1963 about 98 million Americans got polio vaccines
that were contaminated with a monkey virus known as SV40.
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- The U.S. government forced vaccine makers to develop
a virus-free vaccine that was introduced in 1963.
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- The virus was found to cause cancer in laboratory animals,
and studies found DNA from SV40 in some human tumours.
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- It has not been proven to cause cancer in humans.
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- In 1998 researchers at the National Cancer Institute
(NCI) reported that, 30 years after people were exposed to SV40, they found
no increase in the rates of these cancers.
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- Earlier this year Dr. Janet Butel of the Baylor College
of Medicine said there might still be cause to keep an eye on SV40.
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- "The association of SV40 with human cancers is currently
strong enough to warrant serious concern," she wrote in a letter to
the Journal of the National Cancer Institute =97 a letter that prompted
a few newspaper reports alleging a new link between SV40 and cancer.
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- When trying to determine whether something causes a disease,
scientists usually first turn to epidemiology =97 looking at a population
t= o see if people exposed to something, say a toxin, develop that disease
in greater numbers than normal.
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- Any such links have to be verified by finding a mechanism.
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- Durie and Urnovitz said they may have such a mechanism.
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- In a letter to Wednesday's issue of the Journal of the
NCI, they said the SV40 virus caused a type of genetic reshuffling identical
to that seen in a cancer known as multiple myeloma and in Gulf War Syndrome,
a mysterious suite of illnesses that allegedly affects some veterans of
the 1991 Gulf War.
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- "We believe that one of the indirect steps in creating
a cancer cell is that the reshuffled genetic material is reinserted back
into the original genetic material," Urnovitz said. "If the reinsertion
occurs near cancer genes, called oncogenes, the cancer process begins."
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- Durie said the idea might lead to a treatment for any
cancers that might be caused by SV40. "The strategies for treating
cancers have, to date, focused simply on killing the tumour cells. We need
to think in terms of additional attacks on the cells that contain reshuffled
genetic material, and consider that they may be resistant to existing cancer
chemotherapy," he said in a statement.
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