Abstract: Objective To investigate the expression and prognostic value of SRY related high-mobility-group box protein 2 (SOX2) in patients with small cell esophageal carcinoma (SCEC). 
Methods The expression of SOX2 in cancer tissues of SCEC patients was detected by immunohistochemical method, and the expression of SOX2 in normal esophageal mucosa around the cancer was detected. The relationship between SOX2 expression level and clinicopathological parameters was analyzed by Spearman correlation, and Kaplan-Meier survival analysis and COX proportional hazard model were used to analyze the risk factors affecting the prognosis of SCEC. 
Results The positive rate of SOX2 in 118 patients with SCEC was 46.6% (55/118) including 27.1% (32/118) in the high expression group and 19.5% (23/118) in the low expression group. The expression of SOX2 was related to the depth of local invasion, TNM stage, lymph node metastasis and distant metastasis. SOX2 high expression was more common in patients with TNM stage Ⅲ-Ⅳ, local infiltration of fibrous membrane, lymph node metastasis and distant metastasis, while SOX2 low expression was more common in patients with tumor diameter＜2 cm and 2-4 cm, and local infiltration of submucosa and muscularis. Kaplan Meier survival analysis showed that tumor diameter, TNM stage, depth of local invasion, lymph node metastasis, distant metastasis, and high expression of SOX2 were related to the prognosis of patients (P＜0.05). COX proportional hazard model analysis showed that TNM stage, high expression of SOX2, and distant metastasis were independent factors affecting the prognosis of patients. 
Conclusion The high expression of SOX2 can be used as an indicator of poor prognosis in patients with SCEC, and SOX2 is expected to become a prognostic biomarker of SCEC.

Key words: carcinoma, small cell, immunohistochemistry, high mobility group proteins