TERMINALLY ill cancer patients have been given a therapy that uses the herpes virus to destroy cells.
Medics in the UK developed the new treatment which also boosts the immune system.
Patients who participated in the trial in London had a range of cancers.
Medics had exhausted other treatments in these cases, with these patients also having failed to respond to certain immunotherapies.
Experts at The Institute of Cancer Research in London tested the virus on nine patients.
They also tested it on a further 30 patients in combination with immunotherapy nivolumab.
The genetically modified virus was injected directly into the patient's tumours.
It's designed to multiple inside cancer cells to burst them from within.
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It also blocks a protein known as CTLA-4 – releasing the brakes on the immune system and increasing its ability to kill cancer cells.
Three out of nine patients treated with RP2 on its own benefitted from the treatment and saw their tumours shrink.
The medics found that one patient with salivary gland cancer saw his tumour disappear completely and he remains cancer-free - 15 months after starting treatment.
Two patients, one with oesophageal cancer and uveal melanoma found the cancer had spread to the liver.
Through the treatment they saw their cancers shrink and 15 months after treatment, their illness had not progressed.
Seven out of 30 patients who received both RP2 and the immunotherapy nivolumab also benefitted from treatment.
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Of the seven patients receiving the combination who saw a benefit, six remained progression-free at 14 months.
Study leader Professor Kevin Harrington, Professor of Biological Cancer Therapies at The Institute of Cancer Research, London, and Consultant Oncologist at The Royal Marsden NHS Foundation Trust, said it's rare to see such a good response from a study.
"Our study shows that a genetically engineered, cancer-killing virus can deliver a one-two punch against tumours – directly destroying cancer cells from within while also calling in the immune system against them.
“Our initial trial findings suggest that a genetically engineered form of the herpes virus could potentially become a new treatment option for some patients with advanced cancers – including those who haven’t responded to other forms of immunotherapy."
Researchers said that the side effects from the treatment were mild.
They highlighted that none of these side effects were serious enough to have warranted medical attention.
Professor Kristian Helin, Chief Executive of The Institute of Cancer Research, London said viruses can be exploited to kill cancer cells.
He added: "Viruses are one of humanity’s oldest enemies, as we have all seen over the pandemic.
"But our new research suggests we can exploit some of the features that make them challenging adversaries to infect and kill cancer cells. It’s a small study but the initial findings are promising."