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Asbestos exposure is the leading cause of mesothelioma. When inhaled, tiny asbestos fibers can become in lung and other tissues, causing damage at the cellular level. This damage ultimately leads to cancer. Not all people exposed to asbestos will develop mesothelioma, but most people with mesothelioma were exposed to asbestos.
However, there are some mesothelioma patients who were not exposed to asbestos, and the cause remains a mystery. Researchers have suggested other factors like minerals, radiation, and genetics. Another possibility is a virus called SV40. People may have been contaminated through vaccines, resulting in an increased risk for developing mesothelioma.
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 received the 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 signs of infection. However, monkeys with SV40 and suppressed immune systems can experience 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. There was little research on the effects of SV40 between the 1960s and 1990s. However, several researchers began studying the virus and cancer in the 1990s. These studies suggest SV40 could contribute to tumor development in humans, including those tumors that cause mesothelioma. The idea remains controversial, but there could be a connection.
Early Mesothelioma and SV40 Studies
In one study, a researcher injected hamsters with SV40. Each of these infected hamsters developed and died from mesothelioma.
A mesothelioma surgeon joined the study. He 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. Noncancerous control tissue samples from the patients 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 show further evidence it could be a cause of mesothelioma. These studies looked for the virus in mesothelioma patients in Finland, Turkey, Italy, and the United States. No SV40 was found in the Finnish and Turkish samples. However, the American and Italian samples did contain SV40. Because Turkey and Finland never used polio vaccines contaminated with SV40 virus, this helps implicate the virus as a contributing cause of mesothelioma.
Critics of the SV40 Hypothesis
Although research into the connection between SV40 and mesothelioma is intriguing, the idea remains controversial. More than 40 published studies published have found SV40 in various types of tumors. However, other studies have failed to find the connection.
In fact, two studies have failed to find evidence of SV40 in mesothelioma tissue samples. In one of these studies, researchers reported finding no SV40 in 50 biopsy samples. 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 in the studies that did find SV40 in human tumors.
It is possible that public health officials could deny a connection between SV40 and mesothelioma because they do not want the public to panic. When people refuse vaccinations, diseases that have been mostly eradicated can return with a vengeance. Critics of the SV40 cancer link point out that studies that found the virus in tumors also failed to prove there was no laboratory contamination. These researchers also failed to prove SV40 came specifically from the polio vaccine. In addition, there is no evidence that the virus found in the tumors actually caused the cancer. It is possible it was just a passive or benign contaminant.
The International Mesothelioma Interest Group
The International Mesothelioma Interest Group set out to determine if the virus could be consistently found in mesothelioma tissue samples. In a tightly controlled study that included four independent laboratories, researchers found that SV40 was present in most mesothelioma samples. They also proved that the virus did not originate from laboratory contamination. Although the evidence seems strong, critics still disagree that the virus could be a contributing factor in mesothelioma.
Today, research continues to determine the role of SV40 in mesothelioma and other cancers. Some researchers insist it is involved, while others deny that possibility. Whether we will discover the truth remains to be seen. However, for many mesothelioma patients, the cause is no longer an important issue. For them, treatment advancements and options are more important. Researchers are working on that as well. Understanding how a disease like mesothelioma develops is important for prevention, diagnosis, and treatment.
Page Edited by Patient Advocate Dave Foster
Dave has been a mesothelioma Patient Advocate for over 10 years. He consistently attends all major national and international mesothelioma meetings. In doing so, he is able to stay on top of the latest treatments, clinical trials, and research results. He also personally meets with mesothelioma patients and their families and connects them with the best medical specialists and legal representatives available.