A Study of IO Plus Radiotherapy in Patients With Advanced ESCC.

Inclusion Criteria:

1. Age 18-80, had an Eastern Cooperative Oncology Group performance status score of 0-1;
2. Patients had unresectable or recurrent esophageal squamous cell carcinoma that precluded esophagectomy or definitive chemoradiation, or distant metastatic disease;
3. Patients had received no previous systemic therapy (patients who had progressed ≥6 months after \[neo\]adjuvant therapy or definitive chemoradiation were eligible);
4. Patients accepted at least one cycle of anti-PD-1 immunotherapy combined chemotherapy as 1st line treatment.
5. All lesions of current diagnosis did not receive local treatment such as radiotherapy, surgery, radiofrequency ablation before enrollment.
6. The measurable lesion was determined by the investigator based on the RECIST 1.1 assessment. A lesion located in a previous radiotherapy area can be considered a target lesion if it is confirmed to progress and is considered to be measurable according to RECIST 1.1.
7. Estimated survival time \>12 weeks.
8. The function of vital organs meets the following requirements:

   Neutrophil absolute count (ANC) ≥ 1.5 × 10\^9 / L platelets ≥ 100 × 10\^9 / L; Hemoglobin ≥ 9g / dL; serum albumin ≥ 2.8g / dL; Total bilirubin ≤ 1.5 × ULN, ALT, AST and / or AKP ≤ 2.5 × ULN; if there is liver metastasis, ALT and / or AST ≤ 5 × ULN; if there is liver metastasis or bone metastasis AKP ≤ 5 × ULN; serum creatinine ≤ 1.5 × ULN or creatinine clearance \> 60 mL / min; For patients with pulmonary lesions or previous lung irradiation who are known or suspected to have impaired lung function, the forced expiratory volume (FEV1) for 1 second of lung function must be above 1L.
9. Female subjects of childbearing age must have a negative urine or serum pregnancy test within 72 hours prior to randomization. Subjects agreed to adequate contraception during the trial.
10. The patient is voluntarily enrolled and obtained the informed consent form signed by the patient or his legal representative.

Exclusion Criteria:

1. Patients who are prior exposure to immune-mediated therapy.
2. Patients participated in any investigational drug study within 4 weeks preceding the start of treatment.
3. The toxicity of previous anti-tumor treatment has not recovered to ≤ National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE) v5.0 level 1 (except for hair loss) or the level specified by the inclusion/exclusion criteria.
4. Patients with uncontrolled brain metastases, or vertebral body metastasis with spinal cord compression symptoms.
5. Patients with uncontrolled pleural, pericardial or pelvic effusion that requires repeated drainage.
6. Patients with history of immunodeficiency, or severe medical diseases that are not well controlled, which may have effect on the treatment of this study.
7. Any other malignant tumor was diagnosed within 5 years prior to or after the diagnosis of ESCC, except for malignant tumors with a low risk of metastasis and death (5-year survival rate \>90%), such as well-treated basal cells or squamous cell skin cancer or cervical cancer in situ.