A personalised brain cancer vaccine made from patients' own tumours has been shown to extend life by more than a year.
The injected vaccine, combined with standard treatment, proved effective in a US clinical trial involving around 120 patients.
All participants had glioblastoma multiforme tumours, a deadly form of brain cancer which kills 98% of sufferers within five years.
The disease is normally treated with surgery, radiotherapy and chemotherapy, but always recurs.
In the Phase II trial, scientists tested a vaccine based on "heat shock" proteins taken from surgically removed tumours.
Heat shock proteins are produced in response to stress and are highly active in cancer cells.
Compared with 80 untreated patients, the vaccine increased the survival of more than 40 patients by several months on average.
Several patients given the vaccine are still alive after more than a year.
Trial leader neurosurgeon Dr Andrew Parsa, from the University of California at San Francisco, said: "These results are provocative. They suggest that doctors may be able to extend survival even longer by combining the vaccine with other drugs that enhance this immune response."
The results were presented today at the annual meeting of the American Association of Neurological Surgeons in Miami, Florida.
A larger randomised trial comparing the effectiveness of the vaccine with the chemotherapy drug Avastin is to be conducted by the US National Cancer Institute, which began enrolling patients this year.
Each year around 4,700 patients in the UK are diagnosed with malignant brain tumours, and around 4,000 die from the disease.
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