Malignant mesothelioma has long been linked to asbestos exposure. Throughout the last century, thousands of cases of the disease were found in individuals who worked regularly with the toxic mineral in a variety of different jobs. However, a report released about 30 years ago by McDonald and McDonald determined that some 25 to 33 percent of all diagnosed cases of mesothelioma cancer did not have a definitive connection to asbestos exposure; the diagnosed individual was never in contact with asbestos or any sort of asbestos-containing materials.
Over the years, researchers have found a few other potential causes for the development of mesothelioma. One of those may be exposure to the Simian Virus 40 (SV40).
What is SV40?
SV40 is a virus that was first discovered in 1960. It was discovered in the kidney cells of rhesus monkeys. It was found to cause kidney disease and certain cancers in the monkey population. The virus also attacks a particular tumor suppressant gene and interrupts cell death.
Simian Virus 40 came to the attention of the U.S. public when it was determined that these same rhesus monkey kidney cells were being used in the manufacture of polio vaccine that was being given to humans. This particular strain of vaccine was in use from 1958 until 1963 and given to nearly 100 million Americans. A sizeable portion of the vaccines that were administered during that time period was contaminated with Simian Virus 40. Though no exact number has been given as to how many doses may have been contaminated, an estimate stands at somewhere between 10 and 30 million.
SV40 and Mesothelioma
Since the time it was discovered that the Simian Virus 40 could be found in millions of doses of polio vaccine, researchers have been looking for a connection between the virus and cancer development in humans. A few of these studies have found that SV40 is present in many individuals who are diagnosed with mesothelioma disease.
A study led by Dr. Michele Carbone, one of the leading mesothelioma specialists in the U.S., determined that more than half (about 54%) of all malignant mesothelioma cases had SV40 infection within the diseased mesothelial cells. (Carbone, M. "Simian virus 40 and human tumors: It is time to study mechanisms.") However, they did not locate any SV40 contamination among individuals with other types of lung cancer. This reinforced their findings as to a link between SV40 and asbestos cancer, but there was no concluding evidence that linked SV40 alone to mesothelioma. Doctors hypothesized that exposure to asbestos or immunosuppression may have also been involved in these cases.
A similar study conducted in 2008 at the Cancer Research Center of Hawaii and Department of Pathology, University of Hawaii, concluded that while 60 percent of hamsters injected intracardially with Simian Virus 40 died of mesothelioma, the role and significance of SV40 in malignant mesothelioma in humans remains cloudy. (Rivera et al, “The Relationship between Simian Virus 40 and Mesothelioma.”) In summary, the authors reported: “Available evidence appears sufficient to link simian virus 40 either alone or in conjunction with asbestos in causing malignant mesotheliomas; however, it is still insufficient to speculate about the contribution of simian virus 40 to the overall incidence of pleural mesothelioma.”
SV40 and Asbestos
Additional studies which note that the combination of the presence of SV40 and asbestos exposure greatly increases the chance of developing mesothelioma are prevalent as well. In a 2005 report by a number of Italian doctors and scientists (Cristaudo et al, “SV40 Enhances the Risk of Malignant Mesothelioma among People Exposed to Asbestos: A Molecular Epidemiologic Case-Control Study”), the authors hypothesize that SV40 contributes to the development of the cancer only as a co-factor and not as a direct cause.
More importantly, this study determined that “detection of SV40 among a cohort of individuals exposed to asbestos could represent a useful marker to identify those at higher risk for MM. This subgroup of high-risk individuals could be closely monitored for early detection and possibly curative surgical excision.” As doctors continue to search for ways to better diagnose mesothelioma at an earlier stage, identifying high-risk individuals such as these is tantamount to saving more lives.Sources