Scientists have created an “intelligent” surgical knife that can detect in seconds whether tissue being cut is cancerous, promising more effective and accurate surgery in future. The device, built by researchers at London’s Imperial College, could allow doctors to cut back on additional operations to remove further pieces of cancerous tumors. The technology, effectively merging an electrosurgical knife that cuts through tissue using heat with a mass spectrometer for chemical analysis, has also been shown to be able to distinguish beef from horsemeat. Surgeons often find it impossible to tell by sight where tumors end and healthy tissue begins, so some cancer cells are often left behind. A fifth of breast cancer patients who have lumpectomy surgery need a second operation.