A simple breath test can detect changes in people who have undergone surgery for lung cancer, a new study reports.

Researchers found that three chemical markers known as carbonyl compounds, which are gases released when people exhale, were reduced in patients with lung cancer after they had an operation to remove their tumors, compared with before their operations. The findings were published online today (June 9) in the journal The Annals of Thoracic Surgery.

This study demonstrated that levels of certain chemical markers associated with a tumor went down in people after they had surgery for lung cancer, said Dr. Victor van Berkel, a thoracic surgeon at the University of Louisville School of Medicine in Kentucky, who was a co-author of the study. [5 Amazing Technologies That Are Revolutionizing Biotech]

Researchers don't yet know why the compounds detected in the breath samples were reduced. It could be because the tumor that was removed made the compounds, or because the inflammatory process in the body associated with the tumor made them, van Berkel told Live Science.

But the findings suggest that scientists may be able to use these markers in the future as a screening method when they monitor patients after surgery for lung cancer, he said.

Lung cancer is the leading cause of cancer deaths among men and women in the U.S., van Berkel said.

"More people die from lung cancer each year than from breast, prostate and colon cancers combined," he said. If cancer returns in a patient who had surgery, it is helpful to identify this right away, when treatment can be most effective, he explained.

The current screening test used for lung cancer is a chest computed tomography (CT) scan, which involves being exposed to a small amount of radiation. The CT scan can show whether a person has any nodules present on his or her lungs. But if the scan reveals nodules, then follow up invasive testing, such as a biopsy procedure, is needed to figure out whether the nodules are benign or malignant, van Berkel said.

Breath analysis

Unlike a CT scan, taking the breath test used in this new study required each person to give one big exhalation into a balloon-like bag, which collected a 1-liter (34 ounces) sample of air. The bag was connected to a pump that passed the breath over a computer chip that trapped certain chemicals that were present in the air. [Top 10 Cancer-Fighting Foods]

The computer chip was then sent to a lab where the chemicals from the breath were analyzed and quantified. The breath test is not FDA-approved. But someday, it could be a less expensive way to screen for lung cancer compared with a CT scan, and it could be done in a doctor's office, van Berkel told Live Science. The estimated cost of breath test is between $20 and $30 per test, he said.

The breath analysis test was patented in 2010, said van Berkel, who is one of the patent owners.

In this new study, the researchers asked 31 people with lung cancer to take the breath test before and after they had surgery to remove their lung tumors. The researchers compared these patients' results to those of 187 healthy people who were also given the breath test, but who did not have lung cancer.

The breath analysis showed that after the surgery, the average levels for three out of four tumor markers in people who had lung cancer were reduced, and these levels were near the average of those seen in people without lung disease.

Future studies of the device will look at whether it can detect a recurrence of lung cancer — that is, whether the breath test can quickly catch when levels of these tumor markers go back up in people, signaling that the cancer has returned, van Berkel said.

Lung cancer screening

To obtain FDA approval for the test as screening tool for lung cancer, a very large multicenter trial of approximately 7,000 people needs to be done, to show that the breath test is as good a method of identifying lung cancer as CT scans are, van Berkel said. He and his colleagues are in the process of arranging such a clinical trial, which means the breath test is optimistically at least five years away from being used in doctors' offices, he said.

If this technology does get introduced to the market, people with positive breath tests for lung cancer would still need to undergo a CT scan, van Berkel said.

This study brings doctors one step closer to a better test that could help refine lung cancer screening, said Dr. Inga Lennes, director of the pulmonary nodule clinic at Massachusetts General Hospital Cancer Center in Boston, who was not involved in the research.

The problem with existing lung-screening methods, such as CT scans, is that up to 30 percent of people who get the tests are found to have lung nodules, but only a small percentage of those nodules turn out to be cancerous, Lennes said.

The results from this new study still constitute an early finding, and much more work needs to be done before the breath analysis test could be useful in everyday medical practice, Lennes told Live Science. That work includes gaining a better understanding of how the test performs in different circumstances, to determine its best use in different populations, she explained. For example, doctors need to evaluate it as a general screening tool to initially diagnose lung cancer, or as a way to monitor people in both the short and long term after surgery for lung cancer.

The public wants researchers to develop cancer screening methods that are noninvasive and don't involve unnecessary procedures, needles or surgeries, Lennes said.

"Anything that moves us forward to finding lung cancer earlier is a step forward for the whole field," Lennes said.