Increased KL-6 concentrations were observed in IPF-LC patients than pulmonary fibrosis associated with autoimmune diseases (PF-AD) group (p = 0.0022) and ROC curve analysis distinguished these two groups (AUC 71%; 95% CI 54–88; p = 0.0436), indicating a best cut-off value of 1809 U/mL (68% sensitivity, 58% specificity). The gene discussed is MUC1; the disease is pulmonary fibrosis.