Our findings confirmed the predictive value of KL-6 for fibrotic lung involvement and functional impairment in ILD sarcoidosis patients already reported by Miyoshi et al. [20]; however, our study is the first one that shows a significant correlation between a serum biomarker, KL-6, and pulmonary fibrotic lung involvement in sarcoidosis patients, quantified by CPI index. The gene discussed is MUC1; the disease is sarcoidosis.