SBRT Combined With AK104 to Treatment Relapsed or Metastatic ESCC

Inclusion Criteria: 1. age ≥ 18 years. 2. patients enrolled must be eligible for PD-1 treatment-naïve patients with recurrent or metastatic advanced esophageal squamous carcinoma with definite measurable recurrent or metastatic lesions. 3. have at least 2 or more clearly measurable lesions (maximum diameter of lesions≥1 cm and shortest diameter of ≥1.5 cm of lymph nodes according to RECIST v1.1), at least one of which is feasible for radiation therapy). 4. no congestive heart failure, unstable angina, or unstable arrhythmia within the last 6 months. 5. patient activity status score of 0-3 on the Eastern Cooperative Oncology Group (ECOG) scale with a life expectancy assessment of ≥ 3 months. 6. no previous serious abnormalities of hematopoietic, cardiac, pulmonary, hepatic, or renal function and immunodeficiency. 7. absolute T-lymphocyte values ≥ 0.5 times the lower limit of normal and neutrophils ≥ 2.0 × 109/L; AST and ALT ≤ 3.0 times the upper limit of normal (≤ 5.0 times the upper limit of normal for hepatocellular carcinoma/metastatic liver cancer); and creatinine ≤ 3.0 times the upper limit of normal, 1 week before enrollment. 8. patients must have the ability to understand and voluntarily sign the informed consent form. Exclusion Criteria: 1. pregnant gestational or lactating women. 2. those with a history of other malignant diseases in the last 5 years. 3. persons with a history of uncontrolled epilepsy, central nervous system disease, or psychiatric disorder whose clinical severity, as judged by the investigator, may prevent signing an informed consent form or affect patient compliance with medication. 4. clinically significant (i.e., active) heart disease such as symptomatic coronary artery disease, New York Heart Association (NYHA) class II or worse congestive heart failure or severe arrhythmias requiring pharmacologic intervention, or a history of myocardial infarction within the last 12 months. 5. organ transplantation requiring immunosuppressive therapy. 6. Significant active infection or, in the judgment of the investigator, significant hematologic, renal, metabolic, gastrointestinal, endocrine dysfunction or metabolic disorder, or other serious uncontrolled concomitant disease. 7. hypersensitivity to any investigational drug component. 8. have a history of immunodeficiency, including testing positive for HIV or having other acquired or congenital immunodeficiency diseases, or a history of organ transplantation, or other immune-related diseases requiring long-term oral hormone therapy. 9. those who are undergoing acute or chronic TB infection (patients with positive T-spot test and suspicious TB foci on chest radiograph). 10. other conditions that the investigator considers unsuitable for enrollment.