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Summary: Chest x-rays can find lung cancer at an early stage, according to a new report in the Journal of the National Cancer Institute. That's potentially good news, since people have a better chance of surviving lung cancer if it's caught early. However, the researchers say it's still too soon to know for sure whether getting regular chest x-rays can really reduce the number of lung cancer deaths in the US.

Why it's important: Lung cancer is the top cancer killer in the United States, claiming more lives (an estimated 163,000 in 2005 alone) than colon, breast, and prostate cancer combined. One reason lung cancer is so deadly is that it rarely shows any symptoms until it is advanced and difficult to treat. About 60% of lung cancer patients die within a year of diagnosis. When the disease is caught early, though, treatments have a better chance of success. Doctors are looking for ways to find lung cancer early in hopes of helping patients live longer after diagnosis.

What's already known: Numerous studies have tried to determine whether screening for lung cancer -- checking people for the disease even if they have no symptoms -- can help find the disease early and reduce lung cancer deaths. Most of those studies looked at chest x-rays with or without sputum tests (tests of the mucus people cough up). None found any difference in lung cancer deaths when people were screened. But researchers thought these studies may not have had enough people in them to find a small, but potentially important, benefit from screening, as well as being limited in other important ways.

How this study was done: The study is part of the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial, one of the largest screening trials ever done in the US. It was started in 1992 at the National Cancer Institute (NCI) and 10 hospitals across the country. Nearly 155,000 people between the ages of 55 and 74 were recruited. For the lung cancer portion of the trial, about half of them were assigned to get a chest x-ray, while the rest (the control group) got no screening at all. Both groups included current smokers, former smokers, and people who had never smoked.

What was found: Of the 77,465 people assigned to get screened, 5,991 (about 9%) had something suspicious on their initial chest x-ray that required further follow-up. Overall, 126 of those people turned out to have lung cancer, and the disease was caught at stage I in 55 of them. Researchers are still analyzing their data on lung cancer deaths.

"The rate of early cancer detection was better than what we see in the general community," said Christine Berg, MD, one of the NCI researchers conducting the study. "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."

Although the chest x-rays did find early lung cancers, they also found lots of other things that weren't cancer. Only about 2% (1 in 50) of the abnormalities found on the x-rays were actually due to cancer.

"There were a lot of false positives on the initial x-rays," Berg said. "If you get a positive result from a chest x-ray, the message is, don't panic."

For every 1,000 x-rays, only 2 cancers were found in the overall study population (current, former, and nonsmokers together). For every 1,000 x-rays in current smokers, about 6 cancers were found, and among former smokers about 2.4 cancers were found, although the number varied depending on how recently the person had quit (people who had been smoke-free for longer had fewer cancers). Among non-smokers, just 0.4 cancers were found for every 1,000 x-rays.

Those results emphasize the link between smoking and lung cancer, said Robert Smith, PhD, director of cancer screening at the American Cancer Society. And they show the benefit of quitting for reducing lung cancer risk.

"The take-home message is to never start smoking, and if you do smoke, to quit," Berg said.

The bottom line: The study is encouraging because it shows that chest x-rays can, indeed, find lung cancer at an early stage, but researchers still need to determine whether this will translate into a lower death rate from lung cancer. Hopefully, those results will be available at the same time as the final results from the National Lung Screening Trial, a large study that is comparing chest x-rays to spiral computed tomography (CT) for lung cancer screening. Because many people are already getting these tests outside of clinical trials, medical groups and insurance companies are anxiously awaiting the outcome of these studies.

Citation: "Baseline Chest Radiograph for Lung Cancer Detection in the Randomized Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial." Published in the Dec. 21, 2005, issue of the Journal of the National Cancer Institute (Vol. 97, No. 24: 1832-1839). First author: Martin M. Oken, MD, of the Hubert H. Humphrey Cancer Center, North Memorial Medical Center, Robbinsdale, Minnesota.