How SV-40 Virus In Early Polio Vaccines May Cause Cancer
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.
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.
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.
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.
The U.S. government forced vaccine makers to develop a virus-free vaccine that was introduced in 1963.
The virus was found to cause cancer in laboratory animals, and studies found DNA from SV40 in some human tumours.
It has not been proven to cause cancer in humans.
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.
Earlier this year Dr. Janet Butel of the Baylor College of Medicine said there might still be cause to keep an eye on SV40.
"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.
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.
Any such links have to be verified by finding a mechanism.
Durie and Urnovitz said they may have such a mechanism.
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.
"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."
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.