The herpes virus could help to treat the advanced stages of the most serious form of skin cancer, researchers have discovered.

Herpes simplex is the virus that causes cold sores.

Previous laboratory research has shown that a mutant form of the virus has improved the survival times of animals with malignant melanoma tumours.

The virus is also known to reproduce itself more rapidly in human cancer cells, rather than in healthy cells, leading to their death.

A team from the University of Glasgow carried out a preliminary study to discover whether a safe, genetically modified version of the virus could be safely used on patients.

I would hope that herpes simplex might be included in non-surgical therapy for this disease in the future

Two had one injection each of the modified virus, two received two injections and one was given four.

In all three patients who had two or more injections there was evidence of the virus killing tumour cells without invading or harming surrounding tissue.

The most striking effect was seen in the patient who had four injections into two tumours.

Both lumps became flattened and, under a microscope, there were clear signs of cancer cells dying.

'Encouraging' results

Lead researcher Professor Rona MacKie said the results of the trial were "encouraging".

But she warned that the work was still at a very early stage. A widely available treatment could be 10 years away.

She said: "At the moment, other than surgery, we have nothing that works against late-stage melanoma.

"I would hope that herpes simplex might be included in non-surgical therapy for this disease in the future.

"We cannot yet say that it will be, because a lot more work has to be done first."

Professor MacKie said the next stage would be to test whether higher doses of the virus were safe for patients.

Nerve tissue

She said there was only evidence that herpes simplex attacked skin cancer when injected straight into tumours.

She said: "If you put the virus in direct contact with tumour cells it kills them.

"But there are many situations, such as when the cancer has spread to the liver, where this would be difficult."

The herpes virus is naturally attracted to nerve tissue. The cells that give rise to melanoma are derived from the developing nervous system in the foetus, which is thought to be why HSV targets skin tumours.

It also likes to attack actively dividing cells, which is another reason for its affinity with cancer.

Immune response

Dr Richard Sullivan, head of clinical programmes for the Cancer Research Campaign, said the research was one of a number of possible new treatments for melanoma.

Another method involves injecting crushed up cells from the tumour into the bloodstream to stimulate an immune response.

Dr Sullivan said the problem with using viruses was that nobody had successfully managed to penetrate beyond the outer three of four layers of a tumour.

This meant that the virus could potentially kill off small secondary growths, but not larger established primary tumours.

He said: "It may be that we have to aim for a situation where people learn to live with their cancer."

Dr David Kirn, head of Imperial Cancer Research Fund's Viral and Genetic Therapy Programme, said: "It is encouraging to see that a mutant herpes virus has been shown to replicate in one particular tumour type.

"However, this study is in its very early days, so it is important not to raise any false hopes among patients."