A test that predicts which patients with early-stage lung cancer will benefit from chemotherapy has been devised by US scientists.
The test can predict which tumours are most likely to recur
By scanning genes, the scientists were able to identify aggressive cancers which are most likely to return.
This means people at risk could be offered chemotherapy as well as surgery, the New England Journal of Medicine reported.
UK cancer experts said the findings could help provide tailored treatment.
The researchers looked at patients with early-stage non-small cell lung cancer (NSCLC), a form of the disease which accounts for about four out of every five lung cancer cases.
At present, people with the earliest stage cancer, determined by tumour size and whether or not it has not spread beyond the lungs, are offered surgery but not chemotherapy.
However, about 30% of these patients will suffer a recurrence of the disease.
A team based at the Duke University Medical Center, US, looked at the genetic profile of NSCLC tumours.
Dr Anil Potti, who led the research, said: "There are significantly different genetic patterns between the tumours that are likely to recur and those that will not."
The scientists used the genome test to look at the tumours in 129 patients, whose disease statuses were followed over time. They discovered the test predicted the risk of recurrence to a high degree of accuracy.
Dr Potti said: "The current staging system for lung cancer is very crude.
"If a patient went to the doctor with a 2.9cm tumour, the tumour would be removed, but if a patient were to have a 3.1cm tumour, the tumour would be cut out and they would receive chemotherapy too.
"Up to now, everyone knew about 30% of early-stage patients would experience a recurrence, but no-one was able to point out which group may be the most likely to do so."
But if this test were used, he said, people with very early-stage cancer who show a higher likelihood of recurrence could be given chemotherapy as well as surgery.
He said providing this more extensive treatment could potentially save thousands of lives every year.
The test is now due to go into clinical trials in the US and Canada. Fifty medical centres are involved and about 12,000 cancer patients will be included.
Dr Potti said he hoped the results of the trial would be ready in two years' time.
Dr Kat Arney, Cancer Research UK's science information officer, said: "This test has the potential to identify those patients that are likely to benefit from chemotherapy during the early stages of lung cancer.
"Our knowledge of the genes involved in cancer is increasing all the time. In the future, we hope to see tests like this developed for a variety of cancer types.
"They will enable doctors to tailor treatment to suit individual patients, and improve survival.
"We are eager to hear the results of the large clinical trial that is planned, to find out how effective the test is and whether it can save lives."