The goal of this observational study is to to determine whether patients with a high proportion of precursor exhausted T cells (Tpex) in negative tumor draining lymph nodes have longer overall survival. The main question it aims to answer is: Whether precursor exhausted T cells (Tpex) in negative tumor-draining lymph nodes have better predictive efficacy for treatment response than PD-L1 CPS.

Inclusion Criteria:

• Aged ≥18 years
• Histologically confirmed esophageal carcinoma
• Clinical stages IV based on the 8th AJCC TNM classification, or recurrent esophageal cancer
• plan to treated with PD-1 immunotherapy
• Eastern Cooperative Oncology Group(ECOG) performance status: 0-2

Exclusion Criteria:

• Esophageal perforation or hematemesis
• Any active autoimmune disease or a history of autoimmune disease
• Disease progression occurs within 3months after PD-1 immunotherapy.
• Allergic to macromolecular protein preparations, or to any of the ingredients in PD-1 inhibitors for injection.
• Uncontrolled heart diseases or clinical symptoms
• Congenital or acquired immunodeficiency (such as HIV infection); active hepatitis B (HBV-DNA≥104 copy number/ml) or hepatitis C (positive hepatitis C antibody, and HCV-RNA is higher than the detection limit of the analytical method); active tuberculosis.

Advanced or recurrent esophageal squamous cell carcinoma patients