By Kevin Newman (ABCNEWS.com)

Scientists have detected the SV40 virus, which is known to cause cancer in rodents, in human tumors.

It is a mystery with enormous implications that has stumped some of the smartest minds in cancer research:

How did a cancer-causing monkey virus end up in human tumors?

If it is indeed in humans, its role in causing human cancers is unknown. Scientists say it may play a key part - or possibly no part at all. The puzzle began in 1994, when Dr. Michele Carbone, a Loyola University researcher, found the virus SV40, which had never before been detected in humans, in half of the human lung tumors he was studying.

SV40 is known to create tumors in animals, but how it might have gotten into humans was unclear.

"I thought there must be something wrong. I must have made a mistake," he said, remembering the discovery.

Eventually, 60 different lab studies confirmed the results.

"This finding has been replicated in New Zealand, in China, in Britain, in France, in Switzerland, in Belgium," Carbone said.

Several labs did not find any evidence of SV40, and some researchers continue to question Carbone's findings. Efforts in general to explain the SV40 mystery have been hampered by unusual acrimony among those studying the problem.

Could It Have Been Transmitted By Polio Vaccine?

If the monkey virus SV40 is indeed in humans, there are several possible explanations for how it got there, says Janet Butel, a virologist at Baylor College of Medicine and one of America's leading virus researchers.

"One is that it has always been there in humans, and no one has detected it in the past," Butel said.

There is another, much more controversial theory as well, however.

Some researchers contend SV40 was transmitted to humans through the polio vaccine, which has saved many lives. The vaccine is made in monkey kidney cells, and from 1955 to 1963 an estimated 20 million Americans were given doses contaminated with SV40.

Still, the virus was not detected in humans until Carbone's 1994 research, possibly because no one had thought to look for it.

In 1961, the Food and Drug Administration ordered the vaccine's manufacturers to screen out the SV40, which they say they did.

But a lawyer involved in a recent polio case has just published a report claiming contamination continued.

"In certain instances, no [SV40] tests were ever performed," the lawyer, Stan Kops, wrote about one of the vaccine's manufacturers, Lederle.

'Every Batch Was Screened,' Insists Vaccine Maker

Lederle strongly disputes Kops' claim, telling ABCNEWS in a statement "every batch of the polio virus used to manufacture vaccine underwent tissue culture testing for SV40."

If that is true, it suggests another possible reason SV40 has been found in the brain tumors of people born after 1963: transmission from mother to child.

"I think studies need to be done to figure out precisely what the role of the virus might be in human cancer," said Butel.

Scientists specializing in SV40 met today in Bethesda, Md., to sort through some of the controversies.

Some still question whether SV40 truly exists in humans, but the vast majority of scientists attending the conference believe the role of SV40 in humans needs urgent attention.

"We need to find out what it's doing there," said Butel. "It will be a great significance if it's proven to have a role in human cancer because then . it may be possible to block infection and the formation of a tumor."

There may be several viruses linked to cancer in humans.

abcnews.go.com, March 12, 2001

A note about the SV40 virus:

According to Regis Vilchez, M.D., M.Sc., who has studied the SV40 virus,

"There are no commercial tests to evaluate SV40 infection. Serologic assays such as ELISA for SV40 have a low sensitivity. In addition, a recent FDA panel concluded that none of the current ELISA tests for SV40 are reliable for research or diagnostic. While the serum neutralizing antibody test is the recognized gold standard serologic test for SV40, it has low sensitivity and requires great labor.

"Therefore, molecular assays such as polymerase chain reaction (qualitative and quantitative) have been used to study the relation of SV40 infections and human malignancies. These tests are currently for research purposes but different laboratories (including ours) are working to establish them for commercial and diagnostic use. Indeed, this is one of the recommendations of the Institute of Medicine for studies of SV40 in humans. We hope they will be available to patients in the near future."

Additionally, the test is not performed by medical institutions because there is no therapy that can be offered to individuals who may test positive. Individuals who want to be tested for legal reasons should contact a lawyer who works with this issue. Lawyers may be more familiar with labs that may offer this type of service on a case-by-case basis.

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