Lung cancer screening

Lung cancer screening refers to cancer screening strategies used to identify early lung cancers before they cause symptoms, at a point where they are more likely to be curable. More than 224,000 new cases of lung cancer are expected in 2016 with approximately 155,000 deaths expected in 2017. 57% were diagnosedin advanced stages (III and IV) where survival is poor. Screening research addresses potential differences in multiple parameters between groups of research subjects with and without screening. Because there is a substantially higher probability of long-term survival following treatment in localized (55%) than in advanced stage (5%), the specific rationale of lung cancer screening is to diagnose the disease in stage I. Research parameters include population cancer-specific mortality, all-cause mortality, long-term survival following diagnosis of cancer, risks of screening and cost-effectiveness. Screening studies for lung cancer have only been done in high risk populations in the U.S., such as smokers and workers with occupational exposure to certain substances. Results from large randomized studies have recently prompted a large number of professional organizations and governmental agencies in the U.S. to now recommend lung cancer screening in select populations. CT screening has been associated with a high rate of falsely positive tests which may result in unneeded treatment. For each true positive scan there have been as many as 19 falsely positives scans. When screening is done in the context of a process of diagnostic tests, false positives have been reduced to approximately 12%. Other concerns include radiation exposure and the cost of testing along with the follow up of tests. Research has not found two other clinically available tests – sputum cytology or chest radiograph (CXR) screening tests — to reduce the overall number of people who die from lung cancer. Screening studies for lung cancer have only been done in high risk populations in the U.S., such as smokers and workers with occupational exposure to certain substances. In the 2010s recommendations by medical authorities are turning in favour of lung cancer screening, which is likely to become more widely available in the advanced economies. Currently multiple professional organizations as well as the United States Preventive Services Task Force (USPSTF) and the Centers for Medicare and Medicaid Services (CMS) concur and endorse low-dose, computerized tomographic screening for individuals at high-risk of lung cancer. Research has found that regular early screening with two other clinically available tests – sputum cytology and chest radiograph (CXR) — does not have an overall benefit. There is evidence suggesting that regular screening of high-risk smokers and former smokers may reduce the mortality in this particular group of people. More research is necessary to determine the relative risks and benefits for the general public and people who have a low risk of lung cancer. CT screening has been associated with a high rate of falsely positive tests which may result in unneeded treatment. For each true positive scan there have been as many as 19 falsely positives scans. Other concerns include radiation exposure and the cost of testing along with the follow up of tests. False reassurance from false negative findings, overdiagnosis, short term anxiety/distress, and increased rate of incidental findings are other risks. It has been estimated that radiation exposure from repeated screening studies could 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. The National Lung Screening Trial found that screening people who were between 55 and 74 years who had smoked for a long time, and had quit smoking no more than 15 prior to being screened, allows timely intervention to the extent that 16% fewer people died from lung cancer, compared to people who were not screened. Based on this study, the U.S. Preventive Services Task Force recommends annual screening for lung cancer with low-dose computed tomography in adults aged 55 to 80 years who have a 30 pack-year smoking history and currently smoke or have quit within the past 15 years. Screening should be discontinued once a person has not smoked for 15 years or develops a health problem that substantially limits life expectancy or the ability or willingness to have curative lung surgery. This form of screening reduces the chance of death from lung cancer by an absolute amount of 0.3% (relative amount of 20%).