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Researchers have
been discussing accusations that contaminated polio vaccine
stocks are to blame for certain cancers, based on the publication
a month ago of two high-profile papers linking the simian
virus SV40 to human lymphomas.
Less than a week
after the papers were published in March, the US National
Cancer Institute contacted the researchers to establish plans
to send blinded results to three independent labs.
Researchers scanned
99 lymphomas, 235 epithelial tumors and 40 control tissues
for the virus. They found the virus in 43% of non-Hodgkin's
lymphomas, 9% of Hodgkin's lymphomas, and in none of the control
tissues. A second team independently found the virus in 42%
of non-Hodgkin's lymphomas, almost unbelievable agreement.
"These are
very respectable labs with basically identical results,"
said Michele Carbone, associate professor of pathology at
Loyola University in Chicago. The "clear clustering of
positives" is "no accident."
This is not the
first time scientists have linked SV40 to human cancers. Researchers
suggested for years that millions of vials of polio vaccine,
contaminated with SV40, infected individuals between 1953
and 1963 and caused human tumors. Until recently, they were
inevitably met with skepticism, even contempt - and some NCI
researchers published directly contradictory results.
In 1997, the US
National Institutes of Health, with other organizations, organized
an international conference to review the SV40 literature
and address the possibility that the virus causes human tumors.
At the meeting, Carbone, presented his then-controversial
data linking the virus to mesotheliomas. (Since then, more
than 30 independent reports have confirmed his results).
After the meeting,
Carbone says, a conscientious Chicago public health official
contacted Carbone and gave him the last remaining stocks of
polio vaccine from the 1950s. In her paper, Butel isolated
a strain of SV40 from three patients that closely matches
the strain Carbone sequenced from the polio vaccine vials.
The evidence proves
Butel's results are no artifact, Carbone says. "You cannot
contaminate with something that doesn't exist," he said.
"This thing only exists in my freezer."
Since publication
of their research in the Lancet last month, Gazdar and his
colleagues have been investigating rarer subtypes like leukemia
and multiple myelomas. The experiments have not been proceeding
as fast as they would like, Gazdar says, partly because "there's
no government funding" for the research. "The lymphoma
story might force them to fund it."
An important next
step, Gazdar says, is to prove that the SV40 virus causes
lymphomas and isn't just a "passenger" in the cells.
That is no easy task, since researchers have only been able
to isolate the virus in rare instances. For the most part,
they believe, the virus launches a "hit-and-run"
attack, initiating a cascade of tumorigenic events before
it is destroyed by the body.
Still, it is critical
that this research continue, Gazdar says, because molecular
and immunologic data suggest those born after 1963 have also
been exposed to the virus, via horizontal or vertical transmission,
or through sexual contact.
The rates of mesotheliomas,
lymphomas and brain tumors have also all gone up "dramatically"
in the last 30 years. "Coincidence or not, we have to
find out," he said. "It's something to think about."
American
Association of Cancer Research San Francisco, CA April 10,
2002
BMN.com
April 10, 2002
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