The effect of radiographic emphysema in assessing lung cancer risk

Purpose Lung cancer risk models optimise screening by identifying subjects at highest risk, but none of them consider emphysema, a risk factor identifiable on baseline screen. Subjects with a negative baseline low-dose CT (LDCT) screen are at lower risk for subsequent diagnosis and may benefit from risk stratification prior to additional screening, thus we investigated the role of radiographic emphysema as an additional predictor of lung cancer diagnosis in participants with negative baseline LDCT screens of the National Lung Screening Trial. Methods Our cohorts consist of participants with a negative baseline (T0) LDCT screen (n=16 624) and participants who subsequently had a negative 1-year follow-up (T1) screen (n=14 530). Lung cancer risk scores were calculated using the Bach, PLCOm2012 and Liverpool Lung Project models. Risk of incident lung cancer diagnosis at the end of the study and number screened per incident lung cancer were compared between participants with and without radiographic emphysema. Results Radiographic emphysema was independently associated with nearly double the hazard of lung cancer diagnosis at both the second (T1) and third (T2) annual LDCT in all three risk models (HR range 1.9-2.0, p<0.001 for all comparisons). The number screened per incident lung cancer was considerably lower in participants with radiographic emphysema (62 vs 28 at T1 and 91 vs 40 at T2). Conclusion Radiographic emphysema is an independent predictor of lung cancer diagnosis and may help guide decisions surrounding further screening for eligible patients.