WEDNESDAY, Jan. 11 (HealthDay News) -- Lung cancer is the leading cancer killer in the world, and only about 15 percent of cases are diagnosed at an early stage, when it's most treatable.

But two preliminary studies that are scheduled to be presented at a medical meeting this week suggest that scientists are moving closer to developing new screening tests that could potentially detect lung cancer in its earliest stages.

In one report, researchers at Weill Cornell Medical College in New York City evaluated tissue samples from healthy smokers and were able to identify precancerous changes in the cells lining the airways leading to the lungs.

"We found that the earliest molecular changes related to lung cancer are present in the airway epithelium of healthy smokers who do not have any detectable microscopic abnormalities in the lung tissue," said study author Dr. Renat Shaykhiev, an assistant professor of genetic medicine at Weill Cornell.

Shaykhiev added that the findings "may lead to the development of novel strategies to prevent lung cancer development at the very early stages, before the development of clinically detectable cancer."

In the second study, researchers at the University of Texas MD Anderson Cancer Center in Houston developed a blood test that can analyze and determine the exact genetic mutations of circulating tumor cells in a sample size as small as three cells.

"We have developed an extremely sensitive test that could be able to detect mutations present in circulating tumor cells, and we are hoping that from their characterization we would be able to understand diagnostic, prognostic and predictive markers," researcher Heidi Erickson, an assistant professor of thoracic/head and neck medical oncology at MD Anderson, said in an American Association for Cancer Research news release.

"By being able to collect a blood sample from a patient instead of having to do a biopsy, we'll have an opportunity to monitor the patient throughout treatment in an easier way," Erickson said in the release.

One leading lung cancer researcher said the findings, while still very preliminary, are particularly relevant in light of a 2011 groundbreaking study, which showed that screening current and former heavy smokers with three annual low-dose CT scans reduced the risk of death from lung cancer by 20 percent, compared with three annual chest X-rays.

"More than a quarter of patients had one or more pulmonary nodules, but 96 percent of these nodules were not cancer," said Dr. Paul Bunn, the James Dudley chair in cancer research at the University of Colorado School of Medicine, in Denver. "So what we'd like to have is some kind of test that, if you have a CT scan and a nodule is found, would help distinguish whether or not that nodule is cancerous."

Bunn noted that other scientists are working on detecting early lung cancer based on proteins in the blood, as well as volatile organic compounds in breath, and that all of the research is still many years away from yielding commercially available tests.

"We make advances one step at a time and these are first steps, but that's important," Bunn said.

The findings were to be presented this week at a lung cancer meeting in San Diego that was jointly sponsored by the American Association for Cancer Research and the International Association for the Study of Lung Cancer. Data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.

More information

For more on lung cancer, go to the U.S. National Library of Medicine.