A "torch" that can be shone at body organs to see whether they have cancerous growths has just been patented, the Institute of Physics heard this week.

The technique, known as optical biopsy, means that patients can avoid the surgery necessary to discover whether they have cancer, and results are produced at once as the doctor works.

The technique exploits the fact that malignant tissue affects the colour of light shone at it differently from normal tissue.

An optical fibre is inserted through an orifice to the place where the cancer is suspected. Seventy per cent of cancers are near the surface of an organ, allowing the technique to be used. The end of the fibre is held against the tissue and the light is shone at it. The rays enter the tissue and are scattered back to the torch.

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"A second fibre collects the light that comes back out and analyses it, comparing the spectrum of what went in with what came out," said Irving Bigio, of the Los Alamos National Laboratory in New Mexico. "Malignant tissue very clearly affects the colour of the light."

The doctor presses a foot pedal and gets an instant reading about the area being touched with the fibre optic probe, he told the conference, held in Telford.

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Dr Bigio said that the technique has detected colon, bladder, rectal and stomach cancers. It may also be successful for studying cervical lesions.