S100A4 and chronic obstructive pulmonary disease: S100A4, a protein belonging to the S100 family of small calcium-binding proteins, has been demonstrated to be upregulated in various lung diseases, including lung cancer, pulmonary hypertension, idiopathic pulmonary fibrosis (IPF), and obstructive pulmonary disease (COPD), which led to this protein as a potential serum-based biomarker for predicting various lung-related pathologies [46].