Lung cancer is the leading cause of cancer-related death in the world. One of the many reasons for this is that only 25% of patients are diagnosed with early-stage disease that is potentially curable with surgery. Early detection is an important strategy for reducing lung cancer death rates.
Given that cigarette smoking increases lung cancer risk by 20-fold—a risk that persists for years after a person has stopped smoking— smokers are the primary focus for lung cancer screening programs. In 2014, the USPSTF issued the first formal guidance on low-dose CT lung cancer screening, which prevents 20% more lung cancer deaths compared to the chest x-ray. Several recent studies shed light on the benefits and risks of such screenings—including the risk of false-positive findings and the association between lung cancer screening and increased smoking cessation rates.
First formal recommendations
In March 2014, the USPSTF published recommendations on lung cancer screening, urging annual screening with low-dose CT for those age 55 to 80 years who have a 30–pack-year smoking history (for example, a person could have a 30–pack-year history by smoking one pack a day for 30 years or two packs a day for 15 years) and currently smoke or have quit within the past 15 years.3 It is recommended that screening 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.
These recommendations are an important step toward eventual widespread implementation of low-dose CT lung cancer screening in the United States and securing related health insurance coverage, both of which would have a dramatic impact on reducing lung cancer deaths.
New research weighs benefits and harms of screening
In 2011, researchers reported results from the National Lung Screening Trial (NLST) showing that screening with low-dose CT prevents death in one of 320 people screened, but the false-positive rate was high, with 96% of screen-detected abnormalities representing benign lesions (not lung cancer). Since that landmark study, researchers have been looking more closely at the risks and benefits associated with such screening. This research will be critical in informing the design and implementation of nationwide lung cancer screening programs in the future.
Another recent federally funded study explored whether the benefits and harms of low-dose CT screening in the NLST varied according to lung-cancer death risk.4 It found that the 60% of participants with the highest risk for lung-cancer death, based on factors such as age, body-mass index, family history of lung cancer, pack-years of smoking, years since smoking cessation, and emphysema diagnosis, accounted for the great majority (88%) of the lung-cancer deaths prevented by the screening. By contrast, the 20% of participants with the lowest risk of lung-cancer death accounted for only 1% of prevented deaths. These data support refining lung cancer screening criteria to target the highest-risk individuals who stand to benefit the most from lung cancer screening.
Another study, which developed statistical models of screening harms and benefits, affirmed the overall benefits of low-dose CT lung cancer screening.5 The model predicted that 497 deaths would be averted and 5,250 life-years gained per 100,000 people screened. Half of the lung cancers would be detected at an early, more treatable stage. Nevertheless, investigators also noted important screening-related risks, including 67,550 false-positive tests, 910 biopsies or surgeries of benign abnormalities, and 190 overdiagnosed lung cancers (tumors that may never cause any symptoms during a person’s lifetime). False-positive results and overdiagnoses are important potential harms of cancer screening because they contribute to patient anxiety and add to the cost of additional testing.
A recent study addressed the problem of false-positive findings by developing a new diagnostic blood test for lung cancer. The experimental test is noninvasive; it only requires a blood sample, rather than a painful and risky biopsy. By analyzing molecules called microRNA in a patient’s blood, physicians can determine if the abnormality detected on a scan is truly lung cancer. In a large validation study, combination of the microRNA test and low-dose CT resulted in a five-fold reduction of false-positive screening rates (from 19.4% to 3.7%).
Another important benefit of lung cancer screening programs that has emerged is their possible positive effect on smoking cessation. NLST researchers found that smoking cessation was strongly associated with the severity of abnormalities detected in the previous year’s screening; patients were most likely to quit smoking if the screening detected an abnormality that was suspicious for lung cancer and was new or changed from the previous screen. They were least likely to quit if the abnormality detected was not suspicious for cancer. The differences in smoking cessation rates persisted for up to 5 years after the last screen.
The USPSTF recommends counseling and intervention for smoking cessation in all people undergoing lung cancer screening. Integration of smoking cessation programs within lung cancer screening programs would likely further reduce smoking-related deaths.
-Cancerprogress.net
