The Phase Ib stage of this study primarily aims to evaluate the tolerance and safety of TQB6411 Injection in participants with recurrent or metastatic Esophageal cancer who have previously failed treatment with PD-1/PD-L1 monoclonal antibodies combined with platinum-based chemotherapy. The Phase II stage primarily aims to evaluate the efficacy of TQB6411 Injection in this same participants population.

Inclusion Criteria:

• Participants voluntarily participate in this study, sign the informed consent form, and demonstrate good compliance.

• Age between 18 and 75 years old (inclusive)

• Eastern Cooperative Oncology Group (ECOG) score of 0-1

• Expected survival >12 weeks

• At least one measurable lesion per RECIST v1.1

• Laboratory criteria(no hematopoietic growth factor correction within 7 days)：

  • Hemoglobin (HGB) ≥90 g/L;
  • Absolute neutrophil count (NEUT) ≥1.5×10⁹/L;
  • Platelets (PLT) ≥90×10⁹/L;
  • Total bilirubin (TBIL) ≤1.5×ULN;
  • Alanine Aminotransferase (ALT)/Aspartate Aminotransferase (AST) ≤2.5×ULN (≤5×ULN if liver metastases present);
  • Serum creatinine (CR) ≤1.3×ULNorcreatinine clearance rate (CCR) ≥50 mL/min;

• Histologically/cytologically confirmed recurrent or metastatic Esophageal cancer

• Failure/intolerance to prior PD-1/PD-L1 inhibitor plus platinum-based chemotherapy for recurrent/metastatic Esophageal Carcinoma (EC)

• Willingness to provide archived or fresh tumor tissue for biomarker analysis.

• Females of childbearing potential: Negative serum/urine pregnancy test within 7 days before enrollment and agreement to use effective contraception during and for 6 months post-study. Males: Agreement to use effective contraception during and for 6 months post-study.

Exclusion Criteria:

• Current or History of Other Malignancies

• Participants with any condition that may compromise venous access for drug administration or blood sampling are excluded.

• Participants with prior treatment-related adverse reactions that have not recovered to ≤ Grade 1 per CTCAE v5.0 criteria.

• Major surgical procedure or significant traumatic injury within 4 weeks prior to first dose, Scheduled major surgery during the study intervention period, Non-healing wound, ulcer, or bone fracture at screening

• Participants with any bleeding/hemorrhagic event ≥ Grade 3 (per CTCAE v5.0) occurring within 4 weeks before the first dose are excluded

• History of Thromboembolic Events within 6 Months

• Poorly Controlled Active Viral Hepatitis

• Participants with active syphilis infection requiring antimicrobial therapy are excluded

• Participants with any of the following pulmonary conditions are excluded: active tuberculosis, idiopathic pulmonary fibrosis (IPF), organizing pneumonia, drug-induced/radiation pneumonitis requiring treatment, symptomatic active pneumonia, or history of interstitial lung disease (ILD) requiring therapy

• History of Substance Abuse or Psychiatric Disorders

• History of Allogeneic Transplantation (Bone Marrow or Solid Organ)

• History of Hepatic Encephalopathy

• Major Cardiovascular Diseases

• Active or Uncontrolled Severe Infections

• Renal Failure Requiring Dialysis (Hemodialysis/Peritoneal Dialysis)

• History of Immunodeficiency

• Poorly Controlled Autoimmune Disease

• Poorly Controlled Autoimmune Disease & Epilepsy Requiring Treatment

• Poorly Controlled Diabetes

• Tumor-Related Symptoms and Treatment Considerations：

  • Exclusion Criterion - Recent Anticancer Treatment (≤3 Weeks or Within 5 Half-Lives)
  • Recent Use of National Medical Products Administration (NMPA) -Approved Anticancer Traditional Chinese Medicine (≤1 Week Prior to Treatment)
  • Radiologically Confirmed Tumor Encasement of Major Vessels with High Bleeding Risk
  • Uncontrolled Effusions Requiring Repeated Drainage
  • Known to have spinal cord compression, leptomeningeal metastasis/carcinomatous meningitis, or symptomatic brain metastases with less than 4 weeks of symptom/imaging control.

• Known Hypersensitivity to Investigational Drug or Excipients

• Prior Treatment with Topoisomerase I Inhibitor-Based ADCs and/or Irinotecan Chemotherapy

• Prior Participation in Anticancer Clinical Trials Within 4 Weeks

• Investigator-Assessed Safety or Compliance Concerns