An advantage of this design is that it removes a gene, leaving more room to insert other genes that will enhance the ability of the virus to kill the cancer cells it infects.

Since the new virus proliferates selectively in tumours, researchers believe that only a small number of copies of the virus would need to reach a tumour for the treatment to be effective.

It might therefore be possible to inject the modified virus into the bloodstream of patients “ unlike other viral therapies under development, which require injection directly into the tumour.

Prof Lemoine adds: "The virus we are using can replicate in tumour tissue much faster than its predecessors and offers real hope for the future. We plan to test it in clinical trials early next year."

Professor Robert Souhami, Cancer Research UK's Director of Clinical and External Affairs, says: "Although a tumour is derived from a patient's own body, there are key differences between normal cells and cancerous ones which we can exploit in developing new treatments.

"In this case, researchers have targeted cells with a virus which can only replicate and spread infection in the specific environment of a tumour. In tests so far it has proven both potent and selective, although only clinical trials will tell us whether the approach can be an effective treatment in people."

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