Breath test may detect signs of lung cancer: study: A new study suggests that a “simple breath test might reveal if a person has early-stage lung cancer.” Researchers examined patients for suspicious lung lesions using CT scans and then tested their breath for four different carbonyls, which are cancer-specific substances. “Having elevated levels of three of the four carbonyls was predictive of lung cancer in 95 percent of patients, while having normal levels of these substances was predictive of a noncancerous growth in 80 percent of patients, the researchers found.” In addition, carbonyl levels dropped back to normal levels after patients with lung cancer underwent surgery.