USP9X and esophageal squamous cell carcinoma: Moreover, a gradual increase of positive rate in high USP9X protein staining from normal (4.0%) to precancerous (low grade intraepithelial neoplasia: 10.5%, high grade intraepithelial neoplasia: 28.6%) and carcinoma tissues (40.2%) was clearly detected, demonstrating that USP9X protein expression might indicate the progress of ESCC.