Scientists have found traces of a monkey virus that contaminated the polio vaccine in the 1950s in a common form of highly malignant human cancer that has mysteriously doubled in incidence over the past 30 years.

Two studies, published Friday in the British journal Lancet, found a link between the virus, called SV40, and nonHodgkin's lymphomas, a disorder ranked fourth or fifth among cancer deaths in the United States among women and men, respectively.

Results suggest that the virus may playa much wider role in cancer than suspected.
"This finding sheds new light on the possible genesis of (this) important group of malignant disorders," said researchers at Baylor College of Medicine in Texas.

The scientists added that their findings may also offer hope for new therapies for the malignancies.

The Salk polio vaccine, administered by injection in the United States and worldwide from 1955 through 1963, was grown on minced kidney tissue from rhesus monkeys.
At the time, the manufacturing process was considered safe. But in 1960, it was discovered that large batches of the vaccine were contaminated with the simian virus later named SV40. An estimated 90 million Americans received Salk vaccine injections and as many as 30 million were exposed to the virus.