There was a time when doctors would sniff the breath of patients, looking for a yeasty note characteristic of tuberculosis or a sweet smell indicative of diabetes. Now researchers at the Cleveland Clinic could update olfactory diagnostics with a prototype breath detector for lung cancer.

Scientists have long known that cancer cells make distinctive metabolic products, called volatile organic compounds, that are exhaled. The differences between these compounds and ones exhaled by a healthy person can be detected using a combination of gas chromatography and mass spectrometry. But Peter Mazzone, a pulmo­nologist at the Cleveland Clinic, is working on a cheaper approach: a disposable piece of paper with 36 chemically sensitive dye spots. When exposed to a patient's breath, the spots change color; a computer then scans them for a telltale color signature. After tests involving 143 people, some with cancer and some without, the researchers found a color signature characteristic of three out of four actual lung-­cancer patients. To hone the system's accuracy, they are now trying to identify the compounds exhaled by lung patients. With lung cancer killing 160,000 people each year in the U.S., technologies better than CT scans and dangerous needle biopsies are desperately needed.