Airflow limitation and mortality during cancer screening in the National Lung Screening Trial: why quantifying airflow limitation matters.

Abstract

Current eligibility criteria for lung cancer (LC) screening are derived from randomised controlled trials and primarily based on age and smoking history. However, the individual benefits of screening are highly variable and potentially attenuated by co-morbidities such as advanced airflow limitation (AL). To examine the relationship between the presence and severity of AL and screening outcomes. This was a secondary analysis of 18 463 high-risk smokers, a substudy from the National Lung Screening Trial, who underwent pre-bronchodilator spirometry at baseline and median follow-up of 6.1 years. We used descriptive statistics and a competing risk proportional hazards model to examine differences in screening outcomes by chronic obstructive pulmonary disease severity group. The risk of developing LC increased with worsening AL (effect size=0.34, p<0.0001), as did the risk of dying of LC (effect size=0.35, p<0.0001). While those with severe AL (Global Initiative for Obstructive Lung Disease, GOLD grade 3-4) had the highest risk of LC and the highest LC mortality, they also had fewer adenocarcinomas (effect size=-0.20, p=0.008) and a lower surgery rate (effect size=-0.16, p=0.014) despite comparable staging, and greater non-LC mortality relative to LC mortality (effect size=0.30, p<0.0001). In participants with no AL, screening with CT was associated with a significant reduction in LC deaths relative to chest X-ray (30.3%, 95% CI 4.5% to 49.2%, p<0.05). The clinically relevant but attenuated reduction in those with AL (18.5%, 95% CI -8.4% to 38.7%, p>0.05) could be attributed to GOLD 3-4, where no appreciable mortality reduction was observed. Despite a greater risk of LC, severe AL was not associated with any apparent reduction in LC mortality following screening.