An "intelligent" knife that knows when it is cutting through cancerous tissue is being tested in three London hospitals.
Experts believe the wand-like device, the first of its kind in the world, will revolutionise cancer treatment by removing uncertainty from surgery.
In an early study, the "iKnife" identified malignant tissue in cancer patients undergoing operations with 100 per cent accuracy.
After more extensive trials it could be approved for general use in operating theatres within three years.
Surgery is often the best hope of a cancer cure, yet even the best surgeons cannot be sure of removing every part of a tumour.
In the case of breast cancer, more than 20 per cent of the cancerous tissue may be left behind.
This can result in a recurrence of disease, or patients having to undergo repeated operations.
The iKnife helps the surgeon by indicating exactly where the cancerous tissue is, and when it has all been removed.
It could allow surgeons to perform riskier operations, and also has the ability to reveal the original site of a cancer that has spread.
As well as potentially improving cancer survival, the device could save thousands of dollars per patient by cutting the cost of lab tests and follow-up operations.
The device is a hi-tech form of "electric scalpel", a tool routinely used by surgeons that uses electricity to sear through membranes and internal organs.
As the knife cuts, smoke from the burned tissue is pumped through a tube into a mass spectrometer, a machine that uses magnetism to produce a chemical "fingerprint" of the atoms fed into it.
The customised version being tested at St Mary's, Hammersmith and Charing Cross hospitals in London employs a user-friendly "traffic light" display.
Red indicates cancer and green healthy tissue, while yellows shows that a region is still unidentified.
More detailed information can also be obtained.
Using the iKnife, an operating surgeon can learn almost instantly if a suspicious growth is cancerous or benign.
Under normal circumstances, a tissue sample has to be sent away for analysis in the hospital's laboratories, which can still take up to half an hour.
The iKnife's inventor Dr Zoltan Takats, from Imperial College London, said: "The surgeon on the spot has to make a decision on where to cut and what to remove.
"The general solution is intra-operative histology.
"A tissue sample is removed from the patient and sent to the histology lab for analysis.
"But even in vast hospitals it can take 10 to 30 minutes.
"There are also reliability issues - the histology team are in an extreme rush and having to do things as fast as possible.
"We can give feedback to the surgeon in some cases in less than a second.
"This could be a real game-changer for tumour resection surgery."
Results of the preliminary study, involving 91 patients with a variety of cancers, are reported in the journal Science Translational Medicine.
