The research is described in the current issue of The Lancet. One group of researchers looked at hundreds of tumours taken from various cancer patients, and compared them with 68 samples taken from patients with non-Hodgkin's lymphoma (cancer of the lymphatic system). They found genetic ‘footprints’ of the virus in 43 percent of the non-Hodgkin's tumour cells. In other types of tumour, some had no trace of the virus at all, and fewer than 10 percent of most other types tested positive.
Tissue taken from 40 apparently healthy patients produced no positive tests at all. Dr Ali Gazdar, from the University of Texas, who led the research, said the results confirmed earlier research on animals which linked the virus to brain and bone cancers, and uncommon types of lung cancer and lymphoma.
The Lancet also printed the results of a separate experiment, carried out at Baylor College of Medicine in Houston, which tested more than 150 non-Hodgkin's tumours. These researchers found virtually identical results - 42 percent of the tumours had the SV40 ‘footprint’, whereas 186 non-malignant control samples all tested negative.
Despite this evidence linking the virus to the cancer, there is still no proof that SV40 actually causes it in humans, although animal experiments suggest this can happen. In addition, it is not proven that the polio vaccine was the source of the SV40. Some patients born long after the contaminated batches were given have tested positive for the virus, yet scientists are unsure whether it is communicable between humans.
Professor Robin Weiss, from University College London, told BBC News Online it was possible that humans had actually given the virus to monkeys in the first place. He challenged the idea that SV40 has come from monkeys. He said it might be the case that the virus was found in these particular cancer cells simply because they provided favourable conditions for it. Knowing that viruses like to grow in cancer cells, it is possible that this is what is happening here. People search for SV40 in tumours, but Professor Weiss states that there has been no increase in these cancers which might have been expected if polio vaccine was the source.
Non-Hodgkin's lymphoma is a collection of several different cancers of the lymphatic system. The incidence is increasing - perhaps partly due to an aging population. On average, the survival rate is between 50 percent and 70 percent after 5 years. The cause of non-Hodgkin’s lymphoma has for long thought to be viral. Three polyomaviruses (SV40, JC virus, and BK virus) can both infect human beings, and cause tumours in animals.
Regis Vilchez, et al., (2002) Association between simian virus 40 and non-Hodgkin’s lymphoma. Lancet 359, 817-23.
Narayan Shivapurkar et al., (2002) Presence of SV40 sequences in human lymphomas. Lancet 359, 851-52.
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8 March 2002
