SPP1 and idiopathic pulmonary fibrosis: In IPF, a progression index based on 4 biomarkers (osteopontin—OPN, matrix metallopeptidase-7—MMP-7, intercellular adhesion molecule-1—ICAM1, and periostin—POSTN) was found to be superior to the clinical GAP score (gender, age, and lung physiology) in predicting progression at 12 months (37).