'Lung cancer' refers to a cancer originating in the lung, in contrast to a cancer originating elsewhere in the body and spreading to the lung, a process referred to as metastasis. Lung cancer can itself metastasize to other organs. The leading factor that increases a person's risk of developing lung cancer, exposure of the lungs to tobacco smoke, can occur either through purposely inhaling the smoke from burning tobacco (e.g., smoking cigarettes), or through inhaling tobacco smoke emanating from others actively smoking tobacco products — i.e., through so-called active or passive smoking. Risk increases with duration and amount of exposure. Exposure to certain environmental pollutants, radiation and asbestos can also increase the risk of developing lung cancer. Health scientists have identified several different types of lung cancer, not all related specifically to exposure to tobacco smoke.
- "For smokers and former smokers who are age 55 to 74 and who have smoked for 30 pack-years or more and either continue to smoke or have quit within the past 15 years, we suggest that annual screening with LDCT should be offered . . . but only in settings that can deliver the comprehensive care provided to NLST participants."
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 2013, a draft clinical practice guideline by the U.S. Preventive Services Task Force (USPSTF) gave a grade B recommendation and stated "annual screening for lung cancer with low-dose computed tomography (LDCT) in persons at high risk for lung cancer based on age and smoking history". The USPSTF published a systematic review that accompanied the draft clinical practice guideline. In 2004, a clinical practice guideline by the 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 x-ray 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.
Annual x-ray computed tomography for three years of patients 55 and 74 years of age and who had smoked at least 30 pack-years, and, "if former smokers, had quit within the previous 15 years" had reduced mortality according to a randomized controlled trial by the National Lung Screening Trial Research Team:* Mortality in the x-ray computed tomography group 1.3%
- Mortality in the chest radiography group 1.7%
- Number needed to treat 292
- Absolute risk reduction 0.34%
- About 25% of the patients had positive results and about 95% of the positive results were false positives
Mass screening may improve the stage of lung cancers that are detected. The International Early Lung Cancer Action Project cohort study of mass screening with x-ray computed tomography in over 31,000 high-risk patients found that 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, this was an uncontrolled cohort study 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.
Mass screening does not clearly reduce mortality. A cohort study found no mortality benefit from mass screening with x-ray computed tomography. 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. Mass screening with low-dose spiral x-ray computed tomography was not found helpful in the DANTE randomized controlled trial.
Solitary pulmonary nodule
A clinical prediction rule can help guide assessment. On online version of this calculator is available at http://www.nucmed.com/nucmed/SPN_Risk_Calculator.aspx.
Nodules stable over two years time are likely to be benign (but not always). The doubling time for a cancer (a double in volume is a 25% increase in diameter) is usually less than 400 days. The mean doubling time for malignant nodules with a ground glass appearance is 813 days.
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- U.S. Preventive Services Task Force. (2013)Screening for Lung Cancer: U.S. Preventive Services Task Force Recommendation Statement
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