MUC1 and idiopathic pulmonary fibrosis: For instance, in prior investigations on Idiopathic Pulmonary Fibrosis (IPF), epithelial proteins like KL-6, Surfactant protein (SP)-A, SP-D, and other factors, such as those indicating oxidative stress (e.g., serum hydroperoxide), have been proposed as biomarkers capable of distinguishing between stable and progressive disease (e.g., CCL18 in serum) or indicating response to therapy (e.g., Toll interacting protein) [14–17].