S100A4 and esophageal squamous cell carcinoma: Ha et al investigated 116 esophageal squamous cell carcinoma (ESCC) specimens for the expression of 5 CAF markers: fibroblast activation protein, fibroblast-specific protein-1 (FSP1), platelet-derived growth factor receptor (PDGFR) α, PDGFRβ, and α-SMA; the results suggested that FSP1, PDGFRα, and α-SMA were unfavorable prognostic indicators of ESCC [34].