Lung cancer screening


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Overview
Lung cancer screening is a strategy used to identify early lung cancer in people, before they develop symptoms. 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 screening could actually induce carcinogenesis|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.

Screening programs for lung cancer have not demonstrated any clear benefits, so far. Randomized controlled trials are underway in this area to see if decreased long-term mortality can be directly observed from CT screening.

Practice guidelines
In 2007, a clinical practice guideline by American College of Chest Physicians recommended not screening for lung cancer.

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. Earlier studies (Mayo Lung Project and Czechoslovakia lung cancer screening study, combining over 17,000 smokers) showed earlier detection of lung cancer was possible but mortality was not improved. Simply detecting a tumor at an earlier stage may not necessarily yield improved mortality. For example, plain radiography 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 USA-based National Cancer Institute is currently completing a randomized trial comparing CT scans with chest radiographs. 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).

In contrast, a March 2007 study in JAMA found no benefit.. 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.