Serum concentrations of KL-6 have been reported to serve as a sensitive biomarker for the diagnosis and monitoring of therapeutic responses in various ILD, including idiopathic pulmonary fibrosis (IPF), non-specific interstitial pneumonia (NSIP), collagen vascular disease-associated interstitial pneumonia (CVD-IP), hypersensitivity pneumonitis (HP), some types of drug-induced pneumonitis, pulmonary sarcoidosis, Pneumocystis jirovecii pneumonia (PCP), Cytomegalovirus (CMV) pneumonia, and radiation pneumonitis [1-8]. The gene discussed is MUC1; the disease is incontinentia pigmenti.