A comprehensive proteomic analysis of multiple IPF patient cohorts has yielded a model based on the different expression levels of osteopontin (OPN), serum protein D (SPD), intercellular adhesion molecule 1 (ICAM1), and matrix metalloproteinase 7 (MMP7), allowing robust differentiation between progressive and stable IPF 88. Here, SPP1 is linked to idiopathic pulmonary fibrosis.