March 03, 2015
3 min read

Presence of emphysema on CT scans increases lung cancer risk

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Emphysema identified in low-dose CT scans increases the risk for lung cancer regardless of a patient’s smoking history, according to findings from the International Early Lung Cancer Action Program.

Because of the high mortality rate associated with lung cancer, early detection is considered essential. CMS recently finalized guidance to ensure Medicare coverage of annual lung cancer screening with low-dose CT for high-risk individuals who meet age and smoking history criteria.

However, aside from the determination about whether nodules are present, information gleaned from CT scans often is ignored, according to study background.

Claudia I. Henschke, MD, PhD, clinical professor of radiology at Mount Sinai Hospital, and colleagues evaluated the prevalence of lung cancer based on the presence of emphysema identified by CT scans for both high-risk and low-risk individuals. Researchers stratified findings by participants’ age and smoking history.

Researchers enrolled 62,124 participants between 2000 and 2013. All participants were aged 40 to 90 years, and they were asymptomatic for lung cancer.

All participants completed a questionnaire at baseline to detail their smoking history, if any. Those who smoked 100 or more cigarettes in their lifetime were classified as smokers (n = 49,756). Those who had more than one cigarette in the month before enrollment in the study or had quit smoking within a year of enrollment were classified as current smokers (n = 23,415). All others were classified as former smokers (n = 26,341).

Participants who had smoked fewer than 100 cigarettes in their lifetime were deemed “never smokers” (n = 12,368).

Current and former smokers were further divided into three smaller groups based on smoking history. Those with a pack-year total less than 30 were considered “light smokers.” Those with a pack-year total between 30 and 59 were considered “moderate smokers.” Those with a pack-year total of 60 or more were considered “heavy smokers.”

CT scans showed lung cancer was prevalent in 1.4% of current smokers (95% CI, 1.3-1.6), 1.1% of former smokers (955 CI, 1-1.2) and 0.4% for never smokers (95% CI, 0.3-0.6).

Emphysema was identified far more frequently in current smokers (29%) and former smokers (21%) than never smokers (1.6%). Among participants classified as light smokers, the prevalence of emphysema was 17.5% for current smokers and 10.9% for former smokers.

Lung cancer was more prevalent in current smokers with emphysema than without emphysema (2.3% vs 1.1%; OR = 1.8; 95% CI, 1.4-2.2). Lung cancer also was more prevalent among former smokers with emphysema than former smokers without emphysema (1.8% vs. 0.9%; OR = 1.7; 95% CI, 1.3-2.2).

Researchers observed the most notable difference among never smokers, among whom lung cancer was prevalent in 2.6% of participants with emphysema and 0.4% of those without emphysema (OR = 6.3; 95% CI, 2.4-16.9).

The prevalence of lung cancer was identical for smokers and never smokers aged 40 to 50 years (0.2%); however, after age 50 years, the prevalence was always higher for smokers than never smokers.

Among smokers, lung cancer prevalence increased with greater pack-year history. Among current smokers, lung cancer prevalence was 0.6% for light smokers, 1.6% for moderate smokers and 2.8% for heavy smokers. Among former smokers, lung cancer incidence was 0.4% for light smokers, 1.3% for moderate smokers and 2.4% for heavy smokers.

A subset of 3,266 participants had never smoked cigarettes but reported being exposed to secondhand tobacco smoke. Multivariate logistical regression adjusted for gender, age, asthma history and Asian ethnicity yielded an OR of 13.6 (P = .01) for individuals in the two highest quartiles of secondhand smoke exposure.

“Our study demonstrated an increase in the prevalence of lung cancer among those who also had CT evidence of emphysema, thereby demonstrating the importance of identifying emphysema when interpreting a CT scan of the chest,” Henschke and colleagues wrote. “While this increased risk of lung cancer had been previously reported for smokers [in several studies], this is the first such report for never smokers. When emphysema is identified … that (never smoker) has the same prevalence of lung cancer as a smoker. Further … the adjusted odds ratio of emphysema was significantly increased when there was moderate to high secondhand tobacco smoke exposure.” – by Anthony SanFilippo

Disclosure: The researchers report no relevant financial disclosures.