A Randomized, Controlled, Double-Blind, Multicenter Phase III Clinical Trial to Evaluate the Efficacy and Safety of Enlonstobart, With or Without SYS6010 as Adjuvant Therapy, in Participants With Pathologically Residual Esophageal Squamous Cell Carcinoma Following Complete Surgical Resection

Inclusion Criteria:

1. Be able to understand and voluntarily sign the written ICF;

2. Age over 18 years, male or female;

3. With histologically/cytologically confirmed esophageal squamous cell carcinoma that is clinically staged as stage II-III , neoadjuvant therapy must be completed prior to randomization, followed by curative surgery for esophageal squamous cell carcinoma, and all of the following criteria must be met:

   Neoadjuvant therapy includes: at least 2 cycles of platinum-based chemotherapy (± immune checkpoint inhibitors) or chemoradiotherapy, with no clinically or radiologically confirmed disease progression during the neoadjuvant therapy phase.

   Participants must have achieved R0 complete resection, with the surgery resulting in a tumor-free state and negative surgical margins.

   Prior to randomization, the Center's Independent Pathology Review Committee (CPIRC) will evaluate the participant's postoperative pathology report (pathology report must be provided). Participants who do not achieve pathological complete response (non-pCR) and have pathological residual disease (ypT1-4aN0M0 or ypT0-4aN+M0) will have their pathology results assessed and confirmed by the Center's Independent Pathology Review Committee in cases of uncertain pathology (e.g., ypNx).

   Postoperative adjuvant therapy must begin 4-16 weeks after curative surgery.;

4. Eastern Cooperative Oncology Group (ECOG) performance status score: 0-1;

5. Life expectancy ≥ 3 months;

Exclusion Criteria:

1. Pathologically diagnosed esophageal carcinoma, including adenocarcinoma, adenosquamous carcinoma, or other histological subtypes;
2. Previous treatment with irinotecan-based agents or topoisomerase I inhibitor-based toxin-conjugated antibody (ADC) drugs; For patients who have received treatment with immune checkpoint inhibitors (e.g., anti-PD-1/PD-L1 monoclonal antibodies) during the neoadjuvant phase: a history of Grade ≥3 immune-related adverse events (irAEs), or a history of irAEs leading to permanent discontinuation of immunotherapy, or a history of immune-related interstitial pneumonia, myocarditis, encephalitis, or severe neurological toxicity of any grade;
3. Patients who have received other anticancer therapies following curative surgery for esophageal squamous cell carcinoma, including chemotherapy, targeted therapy, radiation therapy, biologic therapy, immunotherapy, or treatment with traditional Chinese medicine products approved for such indications; Patients with a known allergy to any component of the SYS6010 product or to humanized monoclonal antibody products;
4. BMI < 16.0 kg/m² or body weight < 40 kg;