Mesothelioma and the Simian Virus 40

Exposure to asbestos is the leading cause of and risk factor for mesothelioma. This fibrous mineral can be inhaled and lodged in lung and other tissues, causing damage at the cellular level that ultimately leads to cancer. Not all people exposed to asbestos will develop mesothelioma, but most people with mesothelioma were exposed to asbestos.

But a few mesothelioma patients were not exposed, and the cause has remained a mystery. Researchers have suggested other minerals, radiation and genes as factors, but there is another possibility: a virus called SV40, which may have contaminated people through vaccines, could increase mesothelioma risk.

What is Simian Virus 40?

Simian virus 40, or SV40, is an infectious pathogen seen in both humans and monkeys. Researchers discovered it as a contaminant in polio vaccines in 1960. Ultimately it was determined that 90 percent of children and 60 percent of adults who got polio vaccine between 1955 and 1963 were given vaccines that contained SV40.

SV40 has since been found in many wild monkey populations, where it is mostly dormant and does not cause any signs of infection. But in monkeys with suppressed immune systems, usually because of another infection, the SV40 virus can cause problems like kidney disease and tumors. SV40 has been used extensively in cancer research because it readily triggers tumors in laboratory animals.

A few early studies concluded SV40 did not cause cancer in humans. SV40’s effects were not studied much between the 1960s and 1990s. Several researchers began studying the virus and cancer in the 1990s, and they suggested SV40 could also contribute to the development of tumors in humans, including those that cause mesothelioma. The idea is still controversial, but some see evidence of a connection.

Early Mesothelioma and SV40 Studies

In one study a researcher injected hamsters with SV40 and found that each one of them developed and died from mesothelioma.

A mesothelioma surgeon got involved in the study and used an extensive collection of biopsy samples from mesothelioma patients to check for the presence of SV40. Sixty percent of those samples contained the virus. Control tissue samples from the patients, which were noncancerous, did not contain the virus. The work of these early researchers has since been replicated in other laboratories around the world.

Additional SV40 Studies Point to Polio Vaccines

More recent studies of SV40 and cancer have found further evidence that it could be a potential cause of mesothelioma. These studies looked for the virus in mesothelioma patients in Finland, Turkey, Italy, and the U.S. No SV40 was found in the Finnish and Turkish samples. However, the American and Italian samples did contain SV40. This helps to implicate the virus as one cause or a contributing cause of mesothelioma because Turkey and Finland never used polio vaccines contaminated with the SV40 virus.

Critics of the SV40 Hypothesis

Although some research into the connection between SV40 and mesothelioma is intriguing and clearly points this virus as a potential cause of the cancer, the idea remains controversial. More than 40 studies published in journals have found SV40 in various types of tumors, not just mesothelioma, and yet other studies have failed to find the connection.

Just two studies, in fact, have failed to find any evidence of SV40 in mesothelioma tissue samples. In one of these studies, the researchers reported testing 50 biopsy samples and finding no SV40 virus. The government has consistently cited these two papers as evidence that SV40 is not connected to mesothelioma or other types of cancer. Not only did these two studies fail to find the virus, but the authors criticized the methods used and conclusions drawn in the studies that did find SV40 in human tumors.

Public health officials may deny that SV40 causes mesothelioma because they do not want to scare people away from vaccines. When people refuse to be vaccinated, diseases that have been mostly eradicated can return with a vengeance. Critics of the SV40 cancer link point out that the studies that found the virus in tumors failed to prove that there was no laboratory contamination, that it came from the polio vaccine, or that the virus found in the tumors actually caused the cancer or was just a passive or benign contaminant.

The International Mesothelioma Interest Group

The International Mesothelioma Interest Group set out to determine one way or another if the virus could be consistently found in mesothelioma tissue samples. In a study that was tightly controlled, and that included four separate and independent laboratories, the group found that SV40 was in most mesothelioma samples. They also proved that the virus did not come from laboratory contamination. Although the evidence seemed strong, critics still disagreed with the conclusion that the virus could be a contributing factor in mesothelioma.

Today, work continues into the study of SV40 with some researchers insisting it is involved in most cases of mesothelioma and others denying that possibility. Whether we will discover the truth any time soon remains to be seen, but for many patients with mesothelioma, the cause is no longer an important issue. More important to them are advancements in treatments, which researchers are also working on. Understanding how a disease like mesothelioma develops, though, is important. It helps researchers come up with better treatments and it also helps prevention.