Effect of pre existing respiratory conditions on survival of lung cancer patients: A nationwide population-based cohort study

Background: Common diseases with potential to increase the risk of death from lung cancer have so far not been studied in large populations. Methods: We did a population-based retrospective cohort study using nationwide health insurance claims data from 2005 to 2012 in Korea including 205 403 lung cancer patients. Multivariate-adjusted hazard ratios (aHRs) of lung cancer mortality by presence, time intervals with lung cancer diagnosis and combinations of pre-existing chronic obstructive pulmonary disease (COPD), pneumonia, asthma and tuberculosis were calculated using the Cox-proportional hazards model. Results: The total number of person-years of follow-up was 397 780 and 60.2% of patients died (mean survival 23.2 months after lung cancer diagnosis). Lung cancer patients with previous respiratory disease had increased aHR for mortality (COPD, hazard ratio [HR] = 1.32, CI 1.29–1.35; pneumonia, HR = 1.14, CI 1.08–1.19; and asthma, HR = 1.11, CI 1.06–1.16). Risks were positively associated with longer duration of pre-existing disease diagnosis; cases with >5 years since diagnosis compared to <2 years: COPD, HR = 2.91, CI 2.82–3.00; pneumonia, HR = 1.67, CI 1.51–1.85; asthma, HR = 1.56, CI 1.45–1.68; and tuberculosis, HR = 2.03, CI 1.90–2.17. Furthermore, elevated HRs of death were found among patients with multiple pre-existing co-morbidities. Conclusion: Hazards of death from lung cancer are significantly increased in cases with pre-existing lung disease, and worse with longer durations, and with multiple combinations before cancer diagnosis. Patients and physicians should be aware of these meaningful risk/prognostic factors for lung cancer when identifying high-risk patient groups.