Differentiating interstitial lung abnormalities and interstitial lung disease in lung cancer screening

<bold>Introduction:</bold> Interstitial lung abnormalities (ILAs) are common incidental findings in lung cancer screening (LCS). We sought to address challenges in differentiating clinically relevant ILAs and ILDs, highlighted in a recent ERS/ESTS/ESTRO/ESR/ESTI/EFOMP statement, by analysing ILAs identified in the SUMMIT Study, the largest LCS study in Europe <bold>Methods:</bold> Of 11,635 LCS individuals, 417 screen detected ILAs were evaluated using a new simple visual classification system focused on traction bronchiolectasis (categorising non-fibrotic and fibrotic ILA and undiagnosed interstitial lung disease [UILD]); and ground glass opacities (GGO and vessels) quantified by a computer tool CALIPER. An age, sex and smoking history matched control group was analysed alongside the ILA cohort to examine ILA associations with forced vital capacity (FVC), hospitalisations (Students T-Tests) and mortality (Cox proportional hazards models, adjusted for age, sex, smoking history). <bold>Results:</bold> Our visual ILA classification system showed superior interobserver agreement versus existing ILA criteria. Participants with UILD had a 6-fold higher mortality rate, while fibrotic and non-fibrotic ILA subtypes had a 3-fold increased mortality compared to controls. CALIPER-quantified GGO and vessels were increased in ILAs and independently associated with mortality (p=0.02 and p=0.03 respectively); in contrast to baseline FVC (p=0.18). <bold>Conclusion:</bold> We demonstrate a new reproducible classification to characterise prognostically important ILAs and ILDs in LCS, to help facilitate early referral to ILD services. We highlight advantages of quantitative analysis and limitations of FVC in delineating ILA mortality associations.