Experts have developed a vaccine which could be used to block the progress of lung cancer.
Non-small cell lung cancer is hard to treat successfully
A small study has suggested it could delay the recurrence of tumours in patients with the most common form of cancer.
Non-small cell lung cancer accounts for three quarters of cases of the disease in the UK.
Doctors said the research, published in the Journal of the National Cancer Institute was "encouraging".
Currently, treatment options for patients with this type of lung cancer are limited.
Only a fifth of patients are considered suitable for surgery. Others may be given chemotherapy and radiotherapy to treat their disease.
Non-small cell lung cancer kills around 25,000 people each year. Many patients diagnosed with advanced disease survive for less than a year.
Primed to attack
Scientists from the Baylor University Medical Center, Dallas, Texas, who carried out the study, said this was the first time a vaccine had been shown to be effective against this type of cancer.
The researchers followed 43 patients - 10 who had early stage cancer and 33 who had advanced stage cancer.
Surgeons removed their tumours. The patients were then injected with a vaccine that included cells from their tumour and a gene called CM-CSF, which changed the surface of the cells to help the body identify them as cancerous.
The body's immune cells then began to recognise, attack and destroy the cancer cells in the lungs.
The patients were given an injection of the GVAX vaccine every two weeks for three months.
A small number of patients were still free of cancer three years after they were vaccinated.
In others, the vaccine appeared to delay the recurrence of cancer for several months.
Dr John Nemunaitis, who led the research, said: "I can't say this is a cure. But in a small number of people sensitive to this approach, the cancer hasn't come back - for a number of patients for over three years."
But the vaccine did not appear to have any benefit for patients with early stage lung cancer.
The research, which was designed to look at the vaccine's safety, was funded in part by Cell Genesys, a pharmaceutical company that hopes to produce it.
Further research is planned.
Dr Mark Britten, chair of the British Lung Foundation, told the BBC: "These are encouraging findings, but these are very early days."
He added: "This is only a vaccine. It will not prevent lung cancer, but treat it once it has occurred."
Dr Richard Sullivan, head of clinical research for Cancer Research UK, said the study was "encouraging".
He added: "Lung cancer treatment is a very big problem. It's an aggressive cancer that takes years to come up.
"Chemotherapy is very toxic and to kill the cancer, you often end up killing the person.
"Getting the immune system to recognise the lung cancer is an exciting prospect.
"It is very promising, there's no doubt about it."
But he added: "This is a small trial. It needs to be replicated in a large study before we can be sure that it will be beneficial to everybody and is not just a fluke."