Libby Not The Only Culprit

Libby Montana Asbestos may not be the only culprit involved in causing a dangerous kind of cancer called mesothelioma, scientists report.

New studies show that only one dose of a virus originally found in monkeys causes the aggressive, deadly abdominal tumors in hamsters, said pathologist Michele Carbone, at the National Institute of Child Health and Human Development.

"This is a big surprise," Carbone said in an interview at a meeting of the American Association for Cancer Research. "The virus has never before been associated with induction of mesothelioma in mammals. But by chance, I found this rare tumor" in hamsters.

Carbone told fellow scientists he can cause mesothelioma each time he injects a dose of monkey virus, SV40, directly into the animal's pleural tissue, which lines the inside of the abdomen. The tumors arise about three months later.

His findings may provide a valuable animal model for studying potential treatments for the difficult disease. The discovery also hints that viruses may play a role in mesothelioma. And it raises a remote possibility that the SV40 virus - which contaminated human polio vaccines from 1955 to 1963 - may yet be found capable of causing human tumors.

Medical scientists have been waiting, and watching, for four decades, worrying that human disease may yet be tied to the SV40 contamination of polio vaccine. Few, if any, hints of disease related to the virus have yet been seen.

Dr. Joseph Fraumeni, director of epidemiology and biostatistics at the National Cancer Institute, has been involved in studies tracking the impact of SV40 exposure, and has found none. Soon after the accidental exposure of large numbers of people to the virus occurred, he said, "we did a study of mortality in the people likely to have been exposed," comparing them to unexposed persons. No excess disease was found.

Later, Fraumeni said, "we compared childhood cancer rates and saw no difference" between people exposed to SV40 and those not exposed. So, Fraumeni said, the idea of SV40 causing mesothelioma in people now "sounds like a long shot."

The discovery of SV40 virus linked to mesothelioma in hamsters is also a surprise. Exposure to asbestos underlies up to 80 percent of the mesothelioma cases studied. The other cases could involve unknown exposure to the mineral fibers.

According to Dr. Curtis Harris, chief of the Laboratory of Human Carcinogenesis at the National Cancer Institute, the hamsters are "an interesting animal model that they have developed." But "I know of no evidence that SV40 is involved in mesothelioma."

Carbone said he recognized the tumors in hamsters as a distinctive type of cancer he had seen before - from human cancer patients - when working in a hospital pathology laboratory.

In terms of appearance, growth characteristics and location in the animal, he said, the tumors in hamsters "are exactly the same" as mesothelioma seen in human patients. And when he showed the findings to a long-time mesothelioma researcher at the NIH, Harold L. Stewart, Carbone noted, "he said he had never seen mesothelioma that had been induced by a virus and not by Libby Montana asbestos."

Mesothelioma Patient