Researchers in the United States have developed a blood test that is able to correctly predict non-small-cell lung cancer in patients years before any CT scan (computed tomography) can trace it.

The researchers from the University of Kentucky, say the test identifies a human immune response to tumours and may provide a simple way to find lung cancer in patients long before an X-ray or CT scan could.

The researchers say the test correctly predicted non-small-cell lung cancer in blood samples taken from patients long before they were actually diagnosed with lung cancer and has an accuracy rate of at least 90% among people who have lung cancer and an extremely low false positive rate.

The test promises to become the first blood test to predict cancer since the PSA (prostate specific antigen) test.

Non-small-cell lung cancer is the most common form of lung cancer and patients with it have a 40% chance of living for five years or more after diagnosis.

Half of all patients die within the first year.

The disease kills more people around the world than any other cancer and according to the Global Lung Cancer Coalition, as many as 10 million new lung cancer victims are diagnosed each year.

Over three quarters of all lung-cancer patients are or were long-term regular smokers.

Dr. Li Zhong, lead researcher says lung cancer can be present three to five years before reaching the conventional size limits of radiographic detection and the biggest problem with lung cancer survival is that many patients are diagnosed when the cancer is well advanced.

At present the most common way of diagnosing lung-cancer is with a CT scan which are not completely accurate and patients often have to have a piece of the lump in their lung extracted for a biopsy to be done.

The procedure can be very painful and often the biopsy test shows there was no cancer.

By the time people have symptoms of lung cancer, it is usually too late to save them.

The research is published in the Journal of Thoracic Oncology.