Definitive chemoradiotherapy (CRT) is the standard treatment option for unresectable locally advanced esophageal cancer. However, as high as more than 40% of patients with esophageal cancer experienced locoregional recurrence after definitive CRT. Immune checkpoint inhibitors targeting PD-1/PD-L1 and/or CTLA-4 have shown substantial clinical benefits in advanced esophageal cancer. Recently, the combination of immunotherapy with CRT has emerged as a promising strategy to improve clinical outcomes in esophageal cancer. The aim of this study was to evaluate the efficacy and safety of cadonilimab (a bispecific PD-1/CTLA-4 antibody) combined with induction chemotherapy followed by definitive radiotherapy in patients with locally advanced esophageal squamous cell carcinoma.

A total of 46 patients with unresectable, locally advanced ESCC will be enrolled to receive cadonilimab plus induction chemotherapy followed by definitive radiotherapy and then 12 additional cycles of maintenance therapy with cadonilimab.

Patients will receive 2 cycles of 3-weekly schedule of induction chemotherapy, consisting of paclitaxel 135 mg/m2, cisplatin 75 mg/m2, and cadonilimab 10 mg/kg on day 1 prior to CRT. Then all patients will receive standard fractionation radiation therapy scheme: 50.4 Gy in 28 fractions, concurrently with 2 cycles of cadonilimab. After the completion of radiotherapy, patients will then receive 12 additional cycles of cadonilimab.

Inclusion Criteria:

1. Histologically confirmed squamous cell carcinoma of the esophagus;
2. Locally advanced, and absence of distant metastasis disease, confirmed by endoscopic ultrasound (EUS) and PET-CT scan, stage II-IVA (according to UICC TNM version 8);
3. Not suitable for surgery (either for medical reasons or patient's choice);
4. Age at diagnosis 18 to 75 years;
5. No prior cancer therapy;
6. Estimated life expectancy >6 months;
7. Eastern Cooperative Oncology Group performance status ≤ 2
8. No history of concomitant or previous malignancy;
9. The function of important organs meets the following requirements: a. white blood cell count (WBC) ≥4.0×109/L, absolute neutrophil count (ANC) ≥1.5×109/L; b. platelets ≥100×109/L; c. hemoglobin ≥9g/dL; d. serum albumin ≥2.8g/dL; e. total bilirubin ≤1.5×ULN, ALT, AST and/or AKP ≤2.5×ULN; f. serum creatinine ≤1.5×ULN or creatinine clearance rate >60 mL/min;
10. Ability to understand the study and sign informed consent.

Exclusion Criteria:

1. Patients who have been treated previously with anti-tumor therapy (including chemotherapy, radiotherapy, surgery, immunotherapy, etc.);
2. Patients with distant metastasis disease or esophageal fistula at diagnosis;
3. Known or suspected allergy or hypersensitivity to monoclonal antibodies, any ingredients of cadonilimab, and the chemotherapeutic drugs paclitaxel or cisplatin;
4. Patients who have a preexisting or coexisting bleeding disorder;
5. Female patients who are pregnant or lactating;
6. Inability to provide informed consent due to psychological, familial, social and other factors;
7. Presence of CTC grade ≥2 peripheral neuropathy;
8. A history of malignancies other than esophageal cancer before enrollment, excluding non-melanoma skin cancer, in situ cervical cancer, or cured early prostate cancer
9. A history of diabetes for more than 10 years and poorly controlled blood glucose levels;
10. Patients who cannot tolerate chemoradiotherapy due to severe cardiac, lung, liver or kidney dysfunction, or hematopoietic disease or cachexia.
11. Active autoimmune diseases, a history of autoimmune diseases (including but not limited to these diseases or syndromes, such as colitis, hepatitis, hyperthyroidism), a history of immunodeficiency (including a positive HIV test result), or other acquired or congenital immunodeficiency diseases, a history of organ transplantation or allogeneic bone marrow transplantation;
12. A history of interstitial lung disease or non-infectious pneumonia;
13. A history of active pulmonary tuberculosis infection within 1 year or a history of active pulmonary tuberculosis infection more than 1 year ago but without formal anti-tuberculosis treatment;
14. Presence of active hepatitis B (HBV DNA ≥ 2000 IU/mL or 104 copies/mL), hepatitis C (positive for hepatitis C antibody, and HCV-RNA levels higher than the lower limit of the assay).