WASHINGTON -- Most chest X-rays with results that look like lung cancer are really false alarms.

But when X-rays do catch cancer, the disease is usually in an early stage that can still be treated, according to the biggest study ever to address lung-cancer screening.

The government-sponsored study of more than 150,000 seemingly healthy adults found that almost one in 10 subjects had troubling X-ray results. But after further screenings that included biopsies for some, only 2 percent were diagnosed with cancer.

"If you get a positive result from a chest X-ray, the message is 'don't panic,'" said Dr. Christine Berg, who led the study. She said tissue variations and other benign factors can resemble tumors on an X-ray.

But almost half of those positive results were for early-stage cancer, which makes some researchers think more screenings could save lives. But Berg said it's too early to make any recommendations about using chest X-rays as a lung cancer screening tool in the general population.

The results are published in Wednesday's issue of the Journal of the National Cancer Institute.

Some say so-called false-positive results just bring needless anxiety and high health bills. They also warn that a biopsy sometimes causes a collapsed lung.

Lung cancer causes 1 million deaths worldwide every year. When patients begin to have symptoms, the cancers are often advanced and treatment is rarely successful. About 90 percent of lung cancer patients die within two years of diagnosis, according to the article.

• Study Abstract