SOX9 and esophageal squamous cell carcinoma: To determine the association between SOX9 expression and ESCC progression, the expression of SOX9 was examined by immunohistochemistry (IHC) in 155 paraffin-embedded, archived clinical ESCC specimens (Stage I, seven cases; Stage IIa, 70 cases; Stage IIb, 15 cases; Stage III, 56 cases; Stage IV, seven cases) (Supplementary Table 1).