The detrimental effect of quantity of smoking on survival in progressive fibrosing ILD

Background and objective: Patients with progressive fibrosing interstitial lung disease (PF-ILD) are prone to early mortality compared with other phenotypes of ILD. The possible effect of smoking on survival has not been investigated yet. Furthermore, it is unknown what the effect of quantity of smoking is in PF-ILD. In this study, it was determined if quantity of smoking is associated with worse survival in patients with PF-ILD. Methods: Patients meeting the INBUILD trial-criteria for PF-ILD were included in this retrospective cohort study. Pack year (py) was tested as a prognostic variable with a multivariable Cox proportional hazard model. Also, median transplant-free survival was compared between heavy (≥20 pys) and mild-moderate smokers (0.1–19.9 pys). Results: In PF-ILD (N = 377), the unadjusted and adjusted hazard ratio for py were significant, (1.014, 95% confidence interval (CI): 1.006–1.022, P < 0.001; 1.011, CI:1.002–1.021, P = 0.022 respectively). This translates to an 11%, 22%, or 44% higher risk for mortality for patients accumulating 10, 20 or 40 pys, respectively. Heavy smokers demonstrated a median transplant-free survival of 3.0 years, which was significantly reduced compared with mild-moderate smokers (3.8 years, P = 0.035). Additionally, more patients with emphysema were heavy smokers (N = 68) than never (N = 5, P < 0.001) or mild-moderate smokers (n = 21, p < 0.001). Conclusion: In PF-ILD, a pack year is associated with an increased risk of mortality. Furthermore, quantity of smoking is associated with worse survival and higher prevalence of emphysema. Our data indicates that limiting amount of pys will provide a survival benefit in patients developing PF-ILD.