Adjuvant Immunotherapy for Esophageal Squamous Cell Carcinoma

Inclusion Criteria: * Aged ≥18 years. * Histologically confirmed esophageal squamous cell carcinoma. * Preoperative staging of cT1b-cT2N+M0 or cT3-cT4a, any N, M0 (UICC/AJCC TNM staging, 8th edition, 2017), and treated with neoadjuvant therapy using an immunotherapy combined with a taxane and platinum regimen, followed by radical surgical resection. * R0 resection. * Postoperative pathological staging of ≥ypT1 and/or ≥ypN1. * Eastern Cooperative Oncology Group (ECOG) performance status (PS) ≤1. * Physical examination and imaging studies completed within 4 weeks prior to randomization confirming disease-free status, with imaging studies including CT scans of the chest and abdomen. * Normal function of major organs. * Women of childbearing potential and men with partners of childbearing potential must agree to use effective contraception during the treatment period and for 6 months before and after the treatment period. * Willingness of the subject to participate in the study and provision of informed consent. * Good compliance of the subject, with the ability to follow up on efficacy and adverse events/reactions as required by the study plan. Exclusion Criteria: * Presence of blood-borne infectious disease human immunodeficiency virus (HIV). * Presence of psychiatric disorders. * History of any other malignancy within the past 5 years (except for completely cured cervical carcinoma in situ or basal cell or squamous cell carcinoma of the skin). * Treatment in the ICU due to severe complications after radical surgery for esophageal cancer. * Severe anastomotic stricture after surgery, requiring dilation treatment. * Known severe allergy to any component of the study drug. * Presence of other autoimmune diseases, or long-term systemic use of immunosuppressants or corticosteroids; the use of inhaled or topical corticosteroids or equivalent doses of adrenal corticosteroid replacement therapy is permitted. * Active hepatitis B (HBV-DNA ≥ 2000 IU/mL or 10⁴ copies/mL), hepatitis C (positive hepatitis C antibody, and HCV-RNA above the lower limit of detection of the assay). Patients with a hepatitis B copy number ≤ 10³ copies/mL after anti-hepatitis B or C treatment may be considered for enrollment at the discretion of the principal investigator. * Presence of any unstable systemic disease (including active uncontrolled peptic ulcer, active infection, grade 4 hypertension, unstable angina, congestive heart failure, unstable cerebrovascular disease, thromboembolic disease, hepatic, renal, metabolic diseases, or unhealed fractures, wounds as judged by the surgeon). * Patients who are difficult to communicate with or follow up with over the long term. * Women who are breastfeeding. * Currently participating or planning to participate in other clinical trials. * Other situations deemed unsuitable by the physician.