A new blood test can detect if a person has lung cancer before symptoms ever develop, research has shown.
Experts carried out a random controlled trial on more than 12,000 people in Scotland who were at high risk of developing the disease.
They found people who took the test were more likely to be diagnosed with cancer at an early stage.
Chief investigator, Prof Frank Sullivan, said the findings could have "globally significant implications".
Experts hope the test will now be rolled out across Scotland and beyond.
Lung cancer is the most common cancer that kills in Scotland, and is attributed to a quarter of the country's cancer-related deaths.
About 85% of patients in the UK are left undiagnosed until the disease has spread to other parts of the body.
However the Early Detection of Cancer of the Lung Scotland trial found the test could detect the illness four years or more before standard clinical diagnosis.
How did the trial work?
In what is believed to be the largest trial of its kind in the world, 12,209 patients from Glasgow, Lanarkshire and Tayside were recruited to take part.
They were all adults aged 50-75 who were smokers or former smokers.
Of those who received the EarlyCDT lung test and went on to develop lung cancer, 41.1% were diagnosed at an early stage (stage 1 and 2) .
Meanwhile about a quarter (26.8%) of the control group who received standard care were diagnosed early.
This meant there was a 36% reduction in late-stage symptoms in patients who were checked for two years after taking the test.
The trial also showed a lower death rates among people who took the test compared with people in the control group.
Lung cancer-specific deaths were also lower in the group whose blood was tested.
Mr Sullivan, a professor of primary care medicine at the University of St Andrews, said: "These landmark findings are likely to have globally significant implications for the early detection of lung cancer by showing how a simple blood test, followed by CT scans, is able to increase the number of patients diagnosed at an earlier stage of the disease, when surgery is still possible and prospects for survival much higher."
'Saving lives and reducing costs'
The findings were presented at the 2019 World Conference on Lung Cancer hosted by the International Association for the Study of Lung Cancer (IASLC) in Barcelona on Monday.
The trial used technology by immunodiagnostics firm Oncimmune, based in Nottingham, which detects the presence of autoantibodies generated by the body's immune system as a natural defence against cancer cells.
Experts hope the test will be given to another 200,000 patients for further research.
Adam Hill, chief executive officer of Oncimmune, said: "We look forward to working with health authorities in Scotland and beyond to roll out EarlyCDT Lung more widely, with the aim of saving lives and reducing costs for the NHS and other healthcare systems around the world.
"Meanwhile, we are continuing to test our technology on other forms of cancer, including liver, ovarian, breast and prostate, in pursuit of our ambition to build the leading immunodiagnostic platform in the field of oncology."
The trial was sponsored by the University of Dundee and NHS Tayside and co-funded by the Scottish Chief Scientist Office, Scottish government and Oncimmune.