USP21 and esophageal squamous cell carcinoma: Further analysis based on IHC evaluation exhibited that ESCC tumor tissues at advanced statuses of primary tumor (T3-4) or with regional lymph node metastasis (N1-3) had higher levels of USP21 protein compared with those at early primary tumor statuses (T1-2) (Fig. 1D) or without positive lymph nodes (N0) (Fig. 1E).