Treatment could help patients whose cancer has spread
Onyx-15, is a cold virus altered so that it infects and kills only cancer cells and leaves healthy cells alone.
Scientists say it has already produced positive results on liver cancer and they believe it could be safe to test in patients whose cancer has spread.
In the latest experiments they infused the virus into the livers of patients whose cancers had spread there.
Dr Daniel Sze of Stanford University Medical Center in California, said: "Rather than injecting it directly into the tumour using a syringe and needle, where it might not get distributed evenly, we injected it into the artery, so that the flow of blood carries it throughout the liver."
A "phase one" study was carried out on a select group of 35 patients, whose gastrointestinal cancer, mostly colon cancer, had spread into the liver.
None could be cured by surgery and chemotherapy had stopped working for them.
The trial, which was intended to test the safety of the treatment, Dr Sze told a meeting in Baltimore of the Society of Cardiovascular and Interventional Radiology.
The trial showed that not only was it safe, but it helped treat the tumours, he told the assembly that.
Such patients usually live only six to eight months, but the average survival time of this group was just over a year.
Shrinking tumours
Dr Sze said: "The tumours shrank somewhat, but more impressive was that blood tests showed that abnormal proteins being secreted by the tumours either decreased significantly, or became completely undetectable.
"That suggests the tumours, although still visible on the CT scan, are dying or dead."
CT scans showed the livers swelled at first, which could be attributed to inflammation from the treatment.
Dr Sze said Onyx-015 may offer an effective way to treat the cancer without the side-effects of chemotherapy.
He said: "Standard chemotherapy kills some healthy cells along with the cancer.
"This engineered adenovirus is designed to kill only the cancer and not to harm healthy cells."
The adenovirus used to produce the compound is a relative of the common cold virus.
Onyx Pharmaceuticals has tried the treatment in a variety of approaches, including a mouthwash to treat oral cancer and injecting it into tumours.
Dr Sze said his team realised that infusing a virus into the liver could be dangerous.
Such a treatment killed 18-year-old Jesse Gelsinger in 1999 in a gene therapy experiment.
Dr Sze said his team took this into account.
He said: "The maximum dose (used in the Gelsinger case) was something like 25 times as high as our maximum dose."
He explained that although patients had tumours, their liver function was normal.
He said: "We were well aware that if we gave too much stress on the livers they could go into liver failure."