The investigators will evaluate the prevalence of lung cancer associated with ILD and IPF utilizing the Korean Health Insurance Review and Assessment Service (HIRA) database, spanning the period from January 2011 to December 2011. The database (HIRA-NPS-2011-0001) was based on random sampling of outpatients from whole population. The sample cases are total 1,375,842. Among them 670,258 cases (age > 40) were evaluated. Patients with ILDs, IPF, CTD, and COPD will be identified based on the International Classification of Disease-10 (ICD-10) diagnostic codes.