Inclusion Criteria:  Age > 18, had an Eastern Cooperative Oncology Group performance status score of 0-3; Patients had unresectable or recurrent disease that precluded esophagectomy or definitive chemoradiation, or distant metastatic disease; Patients had received no previous systemic therapy (patients who had progressed ≥6 months after [neo]adjuvant therapy or definitive chemoradiation were eligible); Patients accepted at least one cycle of anti-PD-1 immunotherapy as 1st line treatment, combined chemotherapy was allowed.  Patients who provided informed consent by appropriate methods. In dead case, optout will be applicable.  Exclusion Criteria:  Patients who are prior exposure to immune-mediated therapy.