Researchers have found that a genetically-engineered version of the cold sore virus (herpes simplex virus) could treat skin cancer.

T-Vec, the modified herpes virus, is harmless to normal cells but when injected into tumors it replicates and releases substances to help fight the cancer.

The findings, published in the Journal of Clinical Oncology, show the therapy could lengthen survival by years – but only for some melanoma patients.

The treatment is not yet licensed.

Similar “immunotherapy” treatments for melanoma are already available in the US and in Europe, but researchers believe T-Vec would be a welcome addition to these.

It would also be the first melanoma treatment that uses a virus.

The latest study is the largest ever randomized trial of an anti-cancer virus and involved 436 patients from 64 centers in the US, the UK, Canada and South Africa who had inoperable malignant melanoma.

UK trial leader Prof Kevin Harrington, from the Institute of Cancer Research, London, said: “There is increasing excitement over the use of viral treatments like T-Vec for cancer, because they can launch a two-pronged attack on tumors – both killing cancer cells directly and marshalling the immune system against them.

“And because viral treatment can target cancer cells specifically, it tends to have fewer side effects than traditional chemotherapy or some of the other new immunotherapies.”

Although it has not yet been licensed, doctors are excited about the very real prospect of a brand new type of treatment for advanced melanoma – and, in the future, possibly other cancers too.

The idea of using viruses to enter and kill cancerous cells has been gathering scientific pace and kudos.

This latest study in the Journal of Clinical Oncology is the largest ever randomized trial of an anti-cancer virus and provides tantalizing evidence that the treatment concept could soon be moved into the clinic, after decades of work in the lab.

Researchers now want to do more studies to identify which patients might benefit from the treatment and whether it should be used alongside other melanoma drugs that are already approved.

Drug regulators will be watching closely and will soon make a final decision about T-Vec.

Damage to the skin by the sun’s harmful UV rays increases your risk of developing this cancer.