A test that finds damaged genes in the lungs of people considered at high risk of lung cancer might be able to predict who actually develops the deadly disease, U.S. researchers said on Wednesday.

The test is still not accurate enough for widespread use, but could replace risky and expensive X-rays, the researchers said.

“Short of repeatedly X-raying a person’s lungs to look for emerging tumors, there is no way now to screen people at high risk for lung cancer, much less predict who will be diagnosed with the cancer at a later date,” said Steven Belinsky, director of the Lung Cancer Program at the Lovelace Respiratory Research Institute in Albuquerque, New Mexico, who led the study.

“When perfected and validated, this kind of test holds great promise for identifying people with lung cancer early enough to successfully treat them,” he added in a statement.

Writing in the March 15 issue of Cancer Research, Belinsky and colleagues said their test identified 65 percent of patients who developed symptoms of lung cancer within 18 months, but also falsely tagged 35 percent of cancer-free people who volunteered as “controls.”

The test looks at the DNA in lung cells in sputum. Certain genes are known to be silenced or turned off in lung cancer.

Lung cancer is by far the most common cause of cancer death in the United States and much of the world. The American Cancer Society says that in 2006 there will be an estimated 174,470 new cases of lung cancer and it will kill 162,460 people.

Only 15 percent of lung cancer patients survive for more than five years, in part because it causes few symptoms early on and most people are not diagnosed until after the tumors have spread.

“Because most people are diagnosed when their cancer is advanced, they may not benefit from surgery, chemotherapy or radiation, which is why median survival from diagnosis is only 13 months,” said Belinsky.

“But lung tumors that can be surgically removed are associated with a five-year survival rate of more than 60 percent.”

The test looks for chemical silencing of six genes known to be inactivated at different stages of lung cancer development - P16, PAX5-beta, MGMT, DAPK, GATA5 and RASSF1A. Patients with three or more of these silenced genes in sputum had a 6.5-fold increase risk of a lung cancer diagnosis within 18 months.

A patient testing positive for the test would receive a follow-up bronchoscopy or an X-ray to look for tumors, Belinsky said.