SUB1 and cancer: The expression of PC4 was examined by immunohistochemistry (IHC) in 98 ESCCs of the learning cohort (from the Cancer Center of Sun Yat-Sen University), 46 ESCCs of the validation cohort (from Tianjin Medical University Cancer Institute and Hospital) and in 30 control normal esophageal mucosa samples (from the Cancer Center of Sun Yat-Sen University).