Harvey Pass, the chief of thoracic surgery at the National Cancer Institute, in Bethesda, Maryland, was sitting in his laboratory one spring afternoon in 1993 when Michele Carbone ... strode in with an unusual request. Carbone was asking Pass for his help in proving a controversial theory he had developed about the origins of mesothelioma, a deadly cancer. Mesothelioma was virtually unheard of prior to 1950. Pass, one of the world's leading mesothelioma surgeons, knew, like other scientists, that the disease was caused by asbestos exposure. But Carbone ... told Pass that he wondered if the cancer might also be caused by a virus - a monkey virus, known as simian virus 40, or SV40, that had widely contaminated early doses of the polio vaccine, but that had long been presumed to be harmless. In 1961 federal health officials ordered vaccine manufacturers to screen for the virus and eliminate it from the vaccine. Worried about creating a panic, they kept the discovery of SV40 under wraps and never recalled existing stocks. For two more years millions of additional people were needlessly exposed - bringing the total to 98 million Americans from 1955 to 1963. Since 1994 Carbone has written more than twenty studies and reviews investigating SV40's link to human cancer. There is no doubt that SV40 is a human carcinogen," he says. Carbone suggests that the virus works in tandem with asbestos or by itself to transform healthy mesothelial cells into cancerous ones.