Researchers found that a genetically engineered version of the vaccinia virus has trebled the average survival time of people with a severe form of liver cancer, with only mild, flu-like side effects.
Thirty people with hepatocellular carcinoma received three doses of the modified virus code-named JX-594 - directly into their liver tumour over one month, 'New Scientist' reported.
Half the volunteers received a low dose of the virus, the other half a high dose. Members of the low and high-dose groups subsequently survived for, on average, 6.7 and 14.1 months respectively.
Trials several years ago had showed that sorafenib, the best existing medication for this cancer, prolonged life by only three months.
Two of the patients on the highest viral dose were still alive more than two years after the treatment.
"It's a very substantial survival benefit," said Laurent Fischer, president of Jennerex, the company in San Francisco developing the treatment under the trade name Pexa-Vec.
Besides shrinking the primary tumour, the virus was able to spread to and shrink any secondary tumours outside the liver.
"Some tumours disappeared completely, and most showed partial destruction on MRI scans," says David Kirn, head of the study at Jennerex. The destruction was equally dramatic in the primary and secondary tumours.
"This clinical trial is an exciting step forward to help find a new way of treating cancers," said Alan Melcher of the University of Leeds, UK, who was not involved in the study.
The fact that the virus appears able to spread to secondary tumours suggests that simply injecting the virus into the bloodstream may be effective.
A trial to compare this treatment with injecting the virus directly into a tumour is under way.