Inclusion Criteria:
1. Have voluntarily signed a written informed consent form (ICF) prior to the initiation of any study-specific procedures.
2. Be aged ≥18 years, regardless of sex.
3. Have histologically or pathologically confirmed esophageal squamous cell carcinoma (ESCC) that is assessed as unsuitable for definitive treatment modalities (including definitive chemoradiotherapy and/or surgery) according to the American Joint Committee on Cancer (AJCC) TNM Staging System, 9th Edition.
4. Have previously received first-line systemic therapy consisting of an immune checkpoint inhibitor in combination with chemotherapy and have experienced radiographically confirmed disease progression during or after such treatment.
5. Have at least one measurable lesion as defined by RECIST version 1.1, as assessed by the investigator, which has not been previously treated with radiotherapy.
6. Have an Eastern Cooperative Oncology Group (ECOG) Performance Status score of 0 or 1.
7. Have a life expectancy of at least 12 weeks.
8. Have adequate organ and bone marrow function, without receiving blood transfusion, recombinant human thrombopoietin, or colony-stimulating factor treatment within 2 weeks prior to the first dose, as defined by all of the following laboratory criteria:
1. Hematologic function:
Absolute neutrophil count (ANC) ≥ 1.5 × 10⁹/L; Platelet count ≥ 100 × 10⁹/L; Hemoglobin ≥ 90 g/L.
2. Hepatic function:
Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 2.5 × upper limit of normal (ULN); For subjects with baseline liver metastases, AST and ALT ≤ 5 × ULN; Serum albumin ≥ 30 g/L; Total bilirubin (TBIL) ≤ 1.5 × ULN.
3. Renal function:
Creatinine clearance ≥ 50 mL/min, calculated using the Cockcroft-Gault formula.
4. Coagulation function:
International normalized ratio (INR), activated partial thromboplastin time (APTT), and prothrombin time (PT) ≤ 1.5 × ULN.
9. For women of childbearing potential and men with partners of childbearing potential, agree to use highly effective contraception from signing the informed consent form until 6 months after the last dose of study treatment.
10. Be willing and able to comply with all protocol-specified visits, treatment plans, laboratory tests, and other study procedures, and voluntarily participate in the study by providing written informed consent.
Exclusion Criteria:
1. Prior placement of an esophageal or tracheal stent.
2. Presence of a high risk of bleeding or perforation due to obvious tumor invasion into adjacent organs of the esophageal lesion (e.g., aorta or trachea), or the presence of a fistula.
3. Participation in another interventional drug clinical trial within 4 weeks prior to enrollment.
4. Prior treatment with any TROP2-targeted therapy and/or topoisomerase I inhibitors.
5. Any of the following events during prior first-line treatment with a PD-1/PD-L1 inhibitor:
1)Disease progression within 3 months after initiation of treatment; History of Grade ≥3 treatment-related adverse events, Grade 2 immune-related cardiotoxicity, or any grade neurologic or ophthalmologic adverse events related to PD-1/PD-L1 inhibitors; 2)Any adverse event from prior PD-1/PD-L1 inhibitor therapy that had not completely resolved or had not improved to Grade 1 or below before study screening; 3)History of adverse events requiring immunosuppressive treatment other than corticosteroids.
6.History of another malignancy within 5 years prior to enrollment, except for adequately treated carcinoma in situ of the cervix, basal cell carcinoma of the skin, or cutaneous squamous cell carcinoma.
7.Known hypersensitivity to any study drug or any of its excipients.
8.Positive test for human immunodeficiency virus (HIV), history of acquired immunodeficiency syndrome (AIDS), or known active syphilis infection.
9.Active autoimmune disease requiring systemic treatment within 2 years prior to initiation of study treatment, or autoimmune disease considered by the investigator to have a risk of recurrence or require future treatment.
10.History of allogeneic organ transplantation or allogeneic hematopoietic stem cell transplantation.
11.Receipt of a live vaccine within 30 days prior to the first dose of study treatment.
12.Any of the following pulmonary conditions:History of interstitial lung disease (ILD) or non-infectious pneumonitis requiring corticosteroid treatment; Current ILD or non-infectious pneumonitis;Suspected ILD or non-infectious pneumonitis that cannot be excluded by imaging at screening;Clinically significant pulmonary impairment due to concurrent pulmonary diseases, including but not limited to pulmonary embolism within 3 months prior to first dosing, severe asthma, severe chronic obstructive pulmonary disease (COPD), restrictive lung disease, pleural effusion, or autoimmune/connective tissue/inflammatory diseases involving the lungs (e.g., rheumatoid arthritis, Sjögren's syndrome, sarcoidosis);Prior pneumonectomy.
13.Active autoimmune disease that required systemic treatment within the previous 2 years. Hormone replacement therapy is not considered systemic treatment, including:Type 1 diabetes mellitus;Hypothyroidism requiring only thyroid hormone replacement therapy;Adrenal or pituitary insufficiency requiring only physiologic corticosteroid replacement therapy.
14.Active infection requiring systemic therapy within 2 weeks prior to the first study dose.
15.Any severe concomitant disease that, in the investigator's judgment, may compromise subject safety or interfere with study participation, including but not limited to uncontrolled hypertension, severe diabetes mellitus, or active infection.
16.Documented severe dry eye syndrome, severe meibomian gland disease and/or blepharitis, or a history of corneal disorders that may delay corneal healing.
17.Women who are pregnant or breastfeeding; women of childbearing potential with a positive pregnancy test at baseline; or women of childbearing potential unwilling to use highly effective contraception during study treatment and for 6 months after the last dose of study treatment.
18.Any other condition that, in the opinion of the investigator, makes the subject unsuitable for participation in the study.
