The Cleveland device is nonspecific: the researchers did not look for particular compounds in the breath but for patterns of color changes. The best sensors yet for detecting cancer on the breath are also nonspecific: dogs’ noses. A study published last year showed that trained dogs can distinguish between the breath of healthy people and those with lung cancer with 99 percent accuracy. The Cleveland device can detect lung cancer in about three out of four breath samples. “We hope our sensing technology can get close to the nose and can get as accurate results as the dogs do,” says Mazzone.
To improve the accuracy of breath-sensing devices, researchers need to know more about what they’re looking for. The metabolic reactions that make the characteristic compounds found in the breath are complex, says Nicholas Broffman, executive director of the Pine Street Foundation, the cancer-research center in San Anselmo, CA, whose scientists demonstrated dogs’ cancer-sensing ability. “We need to see which compounds are unique to cancer and which are not,” he says, in addition to finding out which compounds are unique to which cancers. Lung cancer isn’t the only cancer that causes detectable changes in the breath. “You don’t want to biopsy everywhere,” says Broffman.
Mazzone expects that future advances in mass spectrometry will make it possible to identify which compounds are characteristic of cancer patients, and of patients with different kinds of cancer. “When we know truly what the chemicals are, then we can go back to easier-to-use sensors [like the calorimetric array] and fine-tune them,” he says, in the hopes of increasing their accuracy. For example, the researchers might find that a group of alkanes occurs only in the breath of ovarian-cancer patients and tailor the dye spots on a colorimetric sensor to these compounds.
The Cleveland Clinic study “validates the idea that cancer could have a smell,” says Broffman. Noting that doctors historically sniffed patients’ breath for yeasty or sweet smells to diagnose tuberculosis and diabetes, Broffman says that “medicine is coming full circle.”