In a worldwide study which was led by the Institute of Cancer Research in the UK, scientists showed that the new treatment allowed some patients with skin cancer to live for more than three years – the benchmark many oncologists use to define a cure.
The therapy – called T-VEC – works by infecting and killing cancer cells while also sparking the immune system into action against tumours.
Currently most cancers are treated with using invasive chemotherapy, radiotherapy and surgery, all of which carry the risk of further harm.
The new therapy has far fewer side effects and does not damage healthy tissue or cells.
While the breakthrough came in skin cancer patients, scientists said it raises hopes that the same process could be used for other cancers.
Charities said the development was ‘exciting’ and offered new hope to many patients.
“Patients showing responses beyond three years is something that up until now, we could only have imagined,” said Gillian Nuttall, Founder of Melanoma UK.
Malignant melanoma is the fifth most common cancer in the UK, with more than 13,000 diagnosed each year. It kills more than 2,000 people each year.
Professor Paul Workman, Chief Executive of The Institute of Cancer Research, London, said: “We may normally think of viruses as the enemies of mankind, but it’s their very ability to specifically infect and kill human cells that can make them such promising cancer treatments.
“In this case we are harnessing the ability of an engineered virus to kill cancer cells and stimulate an immune response.”
The clinical trials, which have been ongoing for more than three years, have been conducted in 64 centres across the UK, US, Canada and South Africa.
The results show that 163 patients with stage three and early stage four melanoma who were treated with T-VEC lived for an average of 41 months. That was compared with an average survival of 21.5 months for 66 patients who were given the current best immunotherapy drugs.
And the response was most pronounced in patients with less advanced cancers, underlining the potential benefit as a first-line treatment for metastatic cancers which cannot be surgically removed.
T-VEC is a modified form of herpes virus which multiplies inside cancer cells and bursts 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.
It has also been modified to remove two key genes so that it can’t replicate within healthy cells. Normal cells detect and destroy T-VEC before it can cause damage – but it replicates easily in cancer cells because their infection defences are compromised by genetic errors.
It is one of a new wave of virus-based drugs to show benefits in cancer trials, and is now the first to do so in a major randomised, controlled phase III trial.
“There is increasing excitement over the use of viral treatments like T-VEC for cancer, because they can launch a two-pronged attack on tumours – both killing cancer cells directly and marshalling the immune system against them,” said Prof Kevin Harrington, Professor of Biological Cancer Therapies at The Institute of Cancer Research.
“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.
Dr Hayley Frend, science information manager at Cancer Research UK, said: “Using a virus to both kill cancer cells and nudge the immune system into attacking them is exciting.
“Previous studies have shown T-VEC could benefit some people with advanced skin cancer but this is the first study to prove an increase in survival. The next step will be to understand why only some patients respond to T-VEC, in order to help better identify which patients might benefit from it.”
The research was also welcomed by British academics who said the results were ‘very promising.’
Prof Leonard Seymour, Professor of Gene Therapies, University of Oxford, said: “This T-Vec study shows powerful stimulus of an anticancer immune response in patients with melanoma skin cancer.
“Increasingly we understand that cancer is characterised by suppression of the immune system within tumour deposits, meaning that cancer vaccines have struggled to create useful responses.
“However T-VEC appears to be able to overcome this suppression. At this stage it’s very promising that this appears to have positive results for melanoma skin cancer.”
Muzlifah Haniff, senior lecturer Senior Lecturer and Honorary Consultant Dermatologist at Newcastle University added: “This study reports another treatment strategy based on harnessing the power of our immune system to destroy melanoma, offering new hope to many patients.”
The trial was funded by the manufacturer of T-VEC, Amgen, and is published in the Journal of Clinical Oncology.