"Ever since the connection between asbestos and mesothelioma was first identified there has been intense focus on finding a secondary cause that would explain why some individuals contract the disease while others who have equal exposure to asbestos do not," said James Manfredi, PhD, Associate Professor of Oncological Sciences at Mount Sinai School of Medicine.
The possibility that SV40 might be this secondary cause came to light when it was discovered that polio vaccines widely used in the 1960's were contaminated with the virus. Recently, many studies have found low levels of SV40 in mesothelioma tumors.
Because SV40 must be present in every cell in order to block the functions of critical tumor suppressor proteins, Dr. Manfredi and colleagues argue that the low levels identified in tumors in earlier studies are insufficient to consider SV40 a cause of the cancers. Rather they explain that the SV40 found in these cells was likely the result of contamination.
"SV40 has been a widely used research model," explains Stuart Aaronson, MD, Professor and Chair of Oncological Sciences at Mount Sinai and co-author of the paper. "Since many DNA vectors used everyday in laboratories all over the world contain a portion of the SV40 genome it must be assumed that any sensitive test for SV40 might find this portion of the SV40 genome if rigorous methods aren't used to exclude contamination."
In the current study, the researchers designed a scrupulous protocol with the specific intent of eliminating any possible contamination. They then used a highly sensitive assay, capable of detecting the virus even if it were only present in one out of 5,000 cells. None of the 69 tumors they tested contained detectable levels of SV40.