Screening for lung cancer with chest X-rays can detect early lung cancer but also can produce many false-positive test results, causing needless extra tests, a new study from the National Cancer Institute shows.

A statistic says that about 170,000 people in the United States are diagnosed with lung cancer each year. Most are diagnosed when their disease is advanced, and nearly 90 percent die within two years.

But catching lung cancer early, when surgery is a treatment option, improves survival substantially, and 70 percent of patients who are diagnosed early may survive at least five years.

Between 1993 and 2001, the investigators enrolled 154,942 men and women who were 55 to 74 years of age. These participants included current and former smokers, as well as individuals who never smoked.

The study was based on the analysis of the results obtained after the first X-ray screening.

"There is no accepted early screening technique for lung cancer," said Christine Berg, lead investigator.

Of the 67,038 men and women who received a baseline chest X-ray upon entering the trial, 5,991 (8.9 percent) had abnormal results that required follow-up. After undergoing additional tests, 126 (2.1 percent of the 5,991 participants with abnormal X-rays) were diagnosed with lung cancer within 12 months of the initial chest X-ray.

"[..]That means there were a lot of false positives on the initial X-rays. If you get a positive result from a chest X-ray, the message is 'don't panic,'" she added.

Still, of the cancers detected, though, 44 percent were stage I, meaning those patients were good candidates for surgery.

"The rate of early cancer detection was better than what we see in the general community. But it remains to be seen if that translates into a mortality benefit. It is too early to make any recommendations regarding chest X-rays as a lung cancer screening tool in the general population," Berg concluded.