Mesothelioma

how to read this sentence ?

Although exposure to asbestos is the primary cause of mesothelioma, a slow-developing cancer, researchers believe that infection by the SV40 virus is a contributing cause, since in the United States 60 percent of tissue samples from mesotheliomas, but none from healthy tissue, contain SV40 please see the above para. whats the meaning of "since in the United States 60 percent of tissue samples from mesotheliomas, but none from healthy tissue, contain SV40" ? i am confusing as the para has too many commas. does it want to say 60 percent of tissue samples contain SV40

Public Comments

1. it means that 60 percent of tissue samples contain SV40 but none from healthy tissue. :D
2. I think it means that samples of healthy tissue do not contain SV40, but 60% of tissue samples from people with meothelioma do contain SV40.
3. 60 percent of tissue samples from mesotheliomas contain SV40, but no tissue samples from healthy tissue contain SV40, therefore researchers believe that infection by the SV40 virus is a contributing cause of mesothelioma.
4. Yes. 60 percent of the tissue samples taken only from mesotheliomas contain SV40. The beginning simply says: mesothelioma is a slow developing cancer. Its main cause is exposure to asbestos. However scientists think SV40 virus also plays an important role because 60% of mesotheliomatic tissue samples contain the virus SV40.
5. it says that 60% of tissues contains SV40!!!!
6. These are the facts that you learn from this paragraph: 1) Mesothelioma is a slow-developing cancer. 2)Exposure to asbestos is the primary cause of Mesothelioma 3) Researchers believe that infection by the virus called SV40 (Simian Virus 40) is also a contributing cause to Mesothelioma. 4) Reason for this belief is: In the United States 60 percent of tissue samples from mesotheliomas contain SV40. 5) Healthy tissues donot contain this virus (SV40). Here is some more info from the National Institute of Health: Simian virus 40 (SV40) is a virus that infects several species of monkeys and typically does not cause symptoms or disease in them. When reports appeared in 1961 that injection of SV40 into hamsters could induce tumors (2-5), the United States government instituted a screening program requiring all new lots of poliovirus vaccine be free of SV40 because of concerns about possible adverse effects on human health. (Earlier lots were not withdrawn from the mass immunization program.) Over the last four decades, an intense research effort has been made to determine whether this route of exposure to SV40 has caused health problems in people, including cancer. In order to resolve why some laboratories detect traces of SV40 in mesothelioma while others do not, an International SV40 Working Group, which included the majority of laboratories studying SV40 in human tissues was formed in 1997. The NCI is continuing to evaluate the possible link between SV40 infection and human cancers through intramural research conducted by the Division of Cancer Epidemiology and Genetics (DCEG), which is still monitoring populations known to have been exposed to SV40-contaminated vaccines.