Lung Cancer Screening: False Positives and True Benefits

Kenneth W. Lin, MD, MPH


July 25, 2019

Editorial Collaboration

Medscape &

This transcript has been edited for clarity.

Hi, everyone. I'm Dr Kenny Lin. I'm a family physician at Georgetown University Medical Center, and I blog at Common Sense Family Doctor.

Four and a half years ago, I recorded my first Medscape commentary on strategies for shared decision-making with patients eligible for low-dose CT scans for lung cancer screening. At that time, few patients were being screened, and only one study, the National Lung Screening Trial (NLST), had shown that screening saved lives. The Centers for Medicare & Medicaid Services had just begun paying for CT scans for persons age 55-77 years with at least a 30 pack-year smoking history who still smoke or quit within the past 15 years. There were also concerns in the primary care community about the NLST's results translating into community practice, and whether false positives, overdiagnosis, and complication rates might be higher outside of a controlled trial setting.

An analysis of data from the 2017 Behavioral Risk Factor Surveillance system in 10 states found that 14% of screening-eligible adults had received a low-dose CT (LDCT) scan for lung cancer in the past 12 months.[1] This modest uptake is probably related to several factors, such as appropriately informed patients declining to be screened and gradual implementation of a relatively new test. On that last point, a recent study[2] provided some reassurance. A survey of 165 US community-based lung cancer screening centers found that screening protocols, findings, and the management of abnormal results were similar to those in academic medical centers.[2] These screening centers developed a variety of mechanisms to ensure that all eligible patients receive a counseling and shared–decision-making visit, and are offered smoking cessation resources, if applicable.

Two more randomized trials of lung cancer screening have confirmed the NLST's findings. In the Multicenter Italian Lung Detection trial,[3] about 4000 participants were randomized to annual or biennial LDCT or no screening for a median of 6 years. After 10 years, lung cancer mortality in the LDCT groups was reduced by 39%, with a number needed to screen of 167 to prevent one lung cancer death. Notably, 1 in 3 participants were younger than age 55, and 1 in 4 had fewer than 30 pack-years of cigarette use. Further publications from this group should provide insight into the benefits and harms of screening lower-risk adults.

In the German Lung Cancer Screening Intervention Study,[4] 4000 adults aged 50-69 years who had smoked at least 15 cigarettes daily for 25 years, or 10 cigarettes daily for 30 years, were randomized to five annual rounds of LDCT or a control group. After about 9 years, there was no statistical difference in lung cancer mortality overall, but an analysis restricted to women found lower lung cancer mortality among screened participants.

A prospective cohort study[5] in 12 southern states evaluated the efficiency of the US Preventive Services Task Force guidelines in identifying people who will develop lung cancer. A lower percentage of smokers who self-identified as African American were eligible for screening than smokers who identified as white, due to a lower number of smoking pack-years among African Americans, and suggested lowering the screening threshold for African Americans to 20 pack-years. However, Dr Otis Brawley, an oncologist at Johns Hopkins University and former chief medical officer at the American Cancer Society, warned against interpreting this study as evidence of a biological difference in lung cancer between black and white individuals. The underlying explanation is much more likely to be cultural or socioeconomic.

Although these new data increase our confidence that lung cancer screening has a net benefit for selected, high-risk patients, they do not make shared decision-making less necessary. Last year, a study[6] suggested that primary care clinicians have too many one-sided discussions, focusing almost exclusively on lung cancer screening benefits. It is essential that we inform patients that many true cancers detected by LDCT—from 18% to 67%, depending on the study—are overdiagnosed and would not have become clinically evident during a patient’s lifetime.[7] Patients with these tumors cannot benefit from cancer detection and can only experience harm. The potential benefits of LDCT may still be worth taking this risk, but it's up to each patient to decide.

This has been Dr Kenny Lin for Medscape Family Medicine. Thank you for listening.

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