A drug that helps the immune system recognize and attack lung cancer cells may improve survival time among patients with advanced disease.
A team from the Cross Cancer Institute in Edmonton, Canada, say preliminary trials on 171 patients showed many were still alive two years later.
They hope the drug will one day be used alongside surgery, chemotherapy and radiotherapy.
Details were presented at the European Society for Medical Oncology Congress.
A larger, phase three trial of the drug is expected to start next year.
Researcher Dr Charles Butts said the drug had produced particularly promising results in patients whose cancer was too advanced for surgery, but had not spread to distant organs.
Standard chemotherapy blasts away at the tumour, and in doing so damages many normal cells.
The new drug is more selective in its effect, priming the immune system to search out and attack only tumour cells.
It does this by targeting an abnormal sugar-protein molecule only found on the surface of tumour cells.
The drug, called L-BLP25, was tested on patients with non-small-cell lung cancer, the commonest form of the disease.
Overall, patients given the vaccine survived on average for 17.4 months, compared to an average of 13 months for those who received only standard care.
But in those patients whose cancer was too advanced for surgery, but which had not spread to other organs, the effect was far more pronounced.
Those who received standard care survived for an average of 13.3 months, but among those who took the new drug 60% were still alive after two years. One patients has been taking the drug for 3.5 years.
Cancer Research UK's Dr Siow Ming Lee, of Cancer Research UK, said: "This small pilot study looks encouraging.
"However this needs to be tested in a properly designed, large randomised phase III trial in order to avoid any possibility of false positive results due to biased patient selection or different prior treatments.
"It is early days yet for this vaccine trial and we need to wait for the results of large randomised trials before we can make any strong recommendation.
"Using a person's own immune response to fight cancer is a very interesting approach but we are yet make any significant break-throughs using this method."
In the UK 31,000 people are diagnosed with lung cancer every year, and 27,000 people die from the disease.