A breakthrough has been made in the fight against skin cancer after scientists used a genetically engineered herpes virus to successfully treat the condition.
This marks the first time that a phase III trial of viral immunotherapy has definitively shown benefit for patients with cancer.
Researchers at the Institute of Cancer Research, London, and the Royal Marsden NHS Foundation Trust led the trial in the UK, working alongside 64 research centres around the world.
Their results reveal 16.3 per cent of a group of patients given talimogene laherparepvec (T-VEC) showed a durable treatment response of more than six months, compared with 2.1 per cent given a control treatment.
Some patients had a response extending beyond three years - a mark often used by oncologists as a proxy for cure in immunotherapy.
Responses to treatment were most pronounced in patients with less advanced cancers and those who had yet to receive any treatment, suggesting T-VEC could be effective as a first-line treatment for metastatic melanoma that cannot be surgically removed.
T-VEC, which is a modified form of herpes simplex virus type-1, combats cancer on two fronts. As well as multiplying inside cancer cells and bursting them from within, it has been genetically engineered to produce a molecule called GM-CSF, which stimulates the immune system to attack and destroy the tumour.
However, the virus does not damage healthy cells as the removal of two key genes means it cannot replicate inside them. Normal cells detect and destroy T-VEC before it can cause damage, whereas cancer cells do not as their defences are compromised by genetic errors.
Kevin Harrington, professor of biological cancer therapies at the Institute of Cancer Research, London, said: "Our study showed that T-VEC can deliver a significant, durable benefit for people with melanoma.
"It is encouraging that the treatment had such a clear benefit for patients with less advanced cancers - ongoing studies are evaluating if it can become a first-line treatment for more aggressive melanomas and advanced disease."