Lung cancer screening refers to strategies used to identify early lung cancers before they cause symptoms, at a point where they are more likely to be curable. Screening refers to the use of medical tests to detect disease in asymptomatic people. Screening studies have only been done in high risk populations, such as smokers and workers with occupational exposure to certain substances. This is because radiation exposure from repeated screening studies could actually induce cancer formation in a small percentage of screened subjects, so this risk should be mitigated by a (relatively) high prevalence of lung cancer in the population being screened.

Practice guidelines

Clinical practice guidelines issued by the American College of Chest Physicians in 2007 recommended against routine screening for lung cancer because of a lack of evidence that such screening was effective.

In 2004, a clinical practice guideline by the U.S. Preventive Services Task Force (USPSTF) gave a grade I recommendation indicating that "the evidence is insufficient to recommend for or against screening asymptomatic persons for lung cancer".

Studies of efficacy

Regular chest radiography and sputum examination programs were not effective in reducing mortality from lung cancer. Previous studies (Mayo Lung Project and Czechoslovakia lung cancer screening study, combining over 17,000 smokers) had shown that early detection of lung cancer was possible with such programs, but mortality was not improved. Simply detecting a tumor at an earlier stage may not necessarily lead to improved survival. For example, plain chest X-ray screening resulted in increased time from diagnosis of cancer until death and those cancers being detected by screening tended to be earlier stages. However, these patients continued to die at the same rate as those who are not screened. At present, no professional or specialty organization advocates screening for lung cancer outside of clinical trials.

A computed tomography (CT) scan can uncover tumors not yet visible on an X-ray. CT scanning is now being actively evaluated as a screening tool for lung cancer in high risk patients, and it is showing promising results. The United States National Cancer Institute is currently completing a randomized trial comparing CT scans with chest radiographs. with results expected in 2010. Several single-institution trials are ongoing around the world.

The International Early Lung Cancer Action Project published the results of CT screening on over 31,000 high-risk patients in late 2006 in the New England Journal of Medicine. In this study, 85% of the 484 detected lung cancers were stage I and thus highly treatable. Mathematically these stage I patients would have an expected 10-year survival of 88%. However, there was no randomization of patients (all received CT scans and there was no comparison group receiving only x-rays) and the patients were not actually followed out to 10 years post detection (the median followup was 40 months). Additional controversy surrounded the study after a 2008 New York Times report found that it had been funded indirectly by the parent company of the Liggett Group, a tobacco company; the use of tobacco industry funds was not disclosed in the paper.

In contrast, a March 2007 study in the Journal of the American Medical Association (JAMA) found no mortality benefit from CT-based lung cancer screening. 3,200 current or former smokers were screened for 4 years and offered 3 or 4 CT scans. Lung cancer diagnoses were 3 times as high, and surgeries were 10 times as high, as predicted by a model, but there were no significant differences between observed and expected numbers of advanced cancers or deaths.

Randomized controlled studies are underway in this area to see if decreased long-term mortality can be directly observed from CT screening.