MUC1 and idiopathic pulmonary fibrosis: Among them there are well-established biomarkers, extensively studied in IPF, including Krebs von den Lungen-6 (KL-6), surfactant protein D (SP-D), matrix metalloproteinase 7 (MMP-7), and more recently introduced biomarkers, less extensively studied, including cancer antigen 19-9 (CA19-9), cancer antigen 125 (CA-125), chemokine (C-C motif) ligand 18 (CCL18) and periostin.