The Prognostic Significance of Cancer-Associated Fibroblasts in Esophageal Squamous Cell Carcinoma

Background: Cancer-associated fibroblasts (CAF) are activated fibroblasts in the cancer stroma and play an important role in cancer progression. Some reports have indicated the correlation between the expression of CAF markers and adverse prognosis in several cancers. However, no reports have studied CAF phenotype and its clinical relevance in esophageal squamous cell carcinoma (ESCC). Methods: We investigated CAF phenotype of ESCC based on histology and immunohistochemical expressions of five CAF markers such as fibroblast activation protein (FAP), smooth muscle actin (SMA), fibroblast-specific protein-1 (FSP1), platelet-derived growth factor receptor (PDGFR alpha), and PDGFR beta in 116 ESCC tissue samples. Besides, we also examined the correlation of the CAF phenotype with clinical relevance as well as other cancer-microenvironment related factors. Results: Histologically immature CAF phenotype was correlated with poor prognosis (p<0.001) and associated with increased microvessel density, increased tumor associated macrophages, and epithelial to mesenchymal transition. CAF markers were characteristically expressed in stromal fibroblast close to tumor cells and the expression pattern of 5 CAF markers was highly heterogeneous in every individual cases. Of five CAF markers, SMA, FSP1, and PDGFR alpha were unfavorable prognostic indicators of ESCC. The number of positive CAF markers was greater in ESCC with immature CAFs than in those with mature ones. Conclusions: Our results demonstrate that histologic classification of CAF phenotype is a reliable and significant prognostic predictor in ESCC. CAF markers have the potential to be diagnostic and therapeutic targets in ESCC.