A simple blood test developed by British scientists could spare patients the anguish of waiting for weeks to find out if they have cancer.
The test, which can accurately diagnose cancer within 24 hours, was hailed yesterday as a potential "game-changer."
The research could eventually lead to an end to the painful biopsies necessary to confirm a diagnosis.
Its creators hope GPs will use it to give patients an early warning that they have the disease - and say it could also save lives, because family doctors will be more willing to carry out a cheap and simple test than have to refer patients to specialists.
Most cancers can be treated if they are spotted early, but survival rates decrease rapidly the later the disease is diagnosed.
Study leader Eric Lim, of the Royal Brompton Hospital in London, said: "We hope this study will be a real game-changer that could ultimately lead to many more lives being saved through earlier diagnosis and treatment for all types of cancer.
"A simple, inexpensive blood test available to GPs who suspect a patient may have cancer would result in significant savings to the NHS and could dramatically improve outcomes for patients."
At the moment, cancer is diagnosed from biopsies - a tissue sample taken by a needle or during minor surgery.
But lung cancer patients need a bronchoscopy, in which a fibre-optic tube is inserted into the lungs through the nose or mouth. This involves long waiting times, costs thousands of pounds and can result in complications for some patients.
But the new test, which identifies DNA from a tumour in the patient's blood, could be used instead of such procedures for many people. The Royal Brompton team, working with researchers from Imperial College London, showed their test worked by analysing blood from 223 patients with known or suspected lung cancer.
The results, presented yesterday at the World Conference on Lung Cancer in Colorado, showed the disease was spotted in 68 per cent of patients.
However, although positive results were 98 per cent accurate, negative results were only 35 per cent accurate, meaning the test cannot yet be used to rule out cancer.
Mr Lim said that at the moment, any test results need to be verified by a biopsy - so more research is needed before doctors can rely on the test alone.
Although the study concentrated on lung cancer patients, the researchers expect it to work for other forms of cancer.
Mr Lim said: "The test is not an alternative to a biopsy for all patients, but when a blood test shows a positive result, this could mean a patient is saved from going through an unnecessary and invasive diagnostic procedure.
"It might also result in patients having earlier imaging scans and beginning treatment sooner. Whilst we are immensely excited about the potential this test has for improving patient care, more research, on a wider scale, is needed to validate our initial findings before it could be used in a clinical setting."
Nell Barrie, from Cancer Research UK, said: "Spotting tumour DNA in the bloodstream is a really promising area of research, and has the potential to give doctors valuable early clues about how to treat people's cancer.
"But this approach is not yet available to patients and it wouldn't replace techniques like biopsies.
"Finding new ways to spot cancer early is crucial, especially for diseases like lung cancer where survival rates urgently need improving."
Another team has developed a blood test that gives an early warning if a stable cancer patient's tumour returns.
According to research published in the journal Nature, US scientists at John Hopkins University in Baltimore showed that their blood test spotted a relapse of pancreatic cancer an average six months before the tumour showed up on a scan.
- Daily Mail