A handheld device can identify cancerous tissue in 10 seconds, according to scientists at the University of Texas, reports BBC.
They say it could make surgery to remove a tumour quicker, safer and more precise.
And they hope it would avoid the "heartbreak" of leaving any of the cancer behind.
Tests, published in Science Translational Medicine, suggest the technology is accurate 96% of the time.
The MasSpec Pen takes advantage of the unique metabolism of cancer cells.
Their furious drive to grow and spread means their internal chemistry is very different to that of healthy tissue.
How it works
The pen is touched on to a suspected cancer and releases a tiny droplet of water.
Chemicals inside the living cells move into the droplet, which is then sucked back up the pen for analysis.
The pen is plugged into a mass spectrometer - a piece of kit that can measure the mass of thousands of chemicals every second.
It produces a chemical fingerprint that tells doctors whether they are looking at healthy tissue or cancer.
The challenge for surgeons is finding the border between the cancer and normal tissue.
In some tumours it is obvious, but in others the boundary between healthy and diseased tissue can be blurred.
The pen should help doctors ensure none of the cancer is left behind.
Remove too little tissue, and any remaining cancerous cells will grow into another tumour. But take too much, and you can cause damage, particularly in organs such as the brain.
Livia Eberlin, an assistant professor of chemistry at the University of Texas, Austin, told the BBC: "What's exciting about this technology is how clearly it meets a clinical need.
"The tool is elegant and simple and can be in the hands of surgeons in a short time."
