These findings suggest that Simian virus 40 (SV40) may "participate" in the development of the blood cancer, say researchers from The University of Texas M. D. Anderson Cancer Center, who presented their findings at the annual meeting of the American Association for Cancer Research.
There is no known etiology for most non-Hodgkin's lymphoma, which has doubled in incidence within the past 30 years, say the researchers.
"We found a strong association between the monkey virus DNA and non-Hodgkin's lymphoma in this study, and now the question is whether the virus DNA is there as an innocent bystander, or if it has a role to play in causing the cancer," says the first author, Felipe Samaniego, M.D., assistant professor in the Department of Lymphoma/Myeloma.
There has been a debate as to whether SV40, which contaminated some batches of polio vaccine in the 1950s and 60s, could cause human cancer, especially after the virus was discovered in human tumors. Given that, the M. D. Anderson researchers looked to see if either DNA from the virus or associated antigens or antibodies could be found in non-Hodgkin's lymphoma.
One reason they looked for evidence of SV40 in non-Hodgkin's lymphoma is because other viruses have been commonly found in this form of lymphoma, including Epstein Barr virus. "The assumption has long been that if only some NHL cases showed signs of virus, the rest may have another virus involved in the development of this lymphoma," says Samaniego. "Now we wonder, which one is most important?"
The research team, which included Suizhao Wang, M.D., Ph.D., and Shu Wang, M.D., both post doctoral fellows in the Department of Lymphoma/Myeloma, examined 55 tumors taken from patients newly diagnosed with the disease who had not yet been treated with chemotherapy. After isolating DNA from the genomes of the cancer cells, the researchers found that 33 of the tumors contained DNA sequences from the anitigen produced by the virus. And 30 of 57 tumors stained positive with antibody that recognizes the large T antigen of SV40.
There is no question that SV40 is a powerful cancer virus in some animals, says Samaniego. In a hamster, for example, the virus causes both lymphomas and mesotheolioma lung cancers, as well as tumors in the brain and bones.
People may pick up the virus by association with infected animals, through a polio vaccine, or even though secretions, such as saliva, from a person already infected, he says. One study suggested that at least five percent of Americans have signs of infection with the monkey virus, says Samaniego.
But he theorizes that the body's immune system normally keeps the virus in check until "a transforming event, inflammation or other disease," says Samaniego. "Then the virus may reactivate and cause cancer."
If SV40 does prove to play a role in development of non-Hodgkin's lymphoma, then treatment aimed at destroying the virus could help prevent its development, he says. "The virus could serve as a target in novel immune-based prevention and therapeutic strategies for non-Hodgkin's lymphoma," Samaniego says. "Although this cancer is quite treatable with a 60 percent cure rate, a new therapeutic strategy would be welcomed."