A blood test so sensitive it can spot a single cancer cell lurking among a billion healthy ones could revolutionise the way doctors monitor and tackle the spread of the disease.
The "liquid biopsy" test will give oncologists a crucial early warning sign if a cancer has – or is likely to – spread.
It will also show if levels of blood-borne cancer cells are falling in response to treatment, so doctors will know swiftly if patients are responding to treatment, rather than waiting crucial months for results of CT scans.
Dr Daniel Haber, chief of Massachusetts General Hospital's cancer centre and one of the test's inventors, said: "If you could find out quickly, 'this drug is working, stay on it', or 'this drug is not working, try something else', that would be huge."
Doctors would be able to administer a drug one day, then sample a teaspoon of blood the next day to see if the circulating tumor cells had gone, he said.
He said the test could also reduce the need for painful tissue sampling involved in needle biopsy diagnosis. The liquid biopsy will be tested on cancer patients in four US hospitals this year.
It is expected to take three to five years to develop the test, which features a microchip covered in almost 80,000 tiny bristles. Researchers then apply a stain to bristles, making the cancer cells glow, allowing them to count them and capture them for analysis.
Boston-based scientists and the drugs firm Johnson & Johnson expect development to cost some £19m. After then it could become available in local surgeries and could be approved and purchased by the NHS for use by British doctors.