Definitive chemoradiotherapy versus surgery for resectable esophageal squamous cell carcinoma after a good response to preoperative chemo-immunotherapy

Inclusion Criteria:

1. Volunteered to participate, cooperated with follow-up visits.
2. Aged 18 - 75 years (inclusive), male or female.
3. Histologically confirmed, resectable locally advanced ESCC, defined as cT1N1-3M0 or cT2-4aN0-3M0 according to the AJCC 8th edition, with cCR or PR achieved after 2-3 cycles of induction chemoimmunotherapy consisting of a permitted PD-1 inhibitor combined with a taxane and a platinum agent.
4. Presence of measurable and/or non-measurable lesions as defined by Japanese Classification of Esophageal Cancer (12th Edition);
5. Eastern Cooperative Oncology Group (ECOG) performance status score of 0-1.
6. Life expectancy ≥ 3 months.
7. The function of major organs meets the following requirements:

   1. Absolute neutrophil count (ANC) ≥ 1.5×10\^9/L;
   2. Platelets ≥ 80×10\^9/L;
   3. Hemoglobin ≥ 9 g/dL;
   4. Serum albumin ≥ 2.8 g/dL;
   5. Total bilirubin ≤ 1.5 × ULN, ALT, AST and/or ALP ≤ 2.5 × ULN;
   6. Serum creatinine ≤ 1.5 × ULN or creatinine clearance ≥ 60 mL/min;
   7. International normalized ratio (INR) and activated partial thromboplastin time (APTT) ≤ 1.5× ULN (subjects on stable doses of anticoagulation therapy, such as low molecular weight heparin or warfarin, and with INR within the expected therapeutic range of the anticoagulant can be screened);
8. Comprehensive baseline staging evaluation prior to induction chemoimmunotherapy, including esophagogastroduodenoscopy with biopsy and/or EUS, contrast-enhanced CT of the neck, chest, and upper abdomen, MRI in patients without contraindications, and an upper gastrointestinal contrast study. PET/CT may be performed when clinically indicated and feasible.
9. Patients of childbearing potential must use a medically approved contraceptive method (such as intrauterine device, contraceptive pills, or condoms) during the study treatment period and within 6 months after the end of the study treatment; serum Human Chorionic Gonadotropin (HCG) or urine HCG test must be negative within 72 hours before study enrollment; and must not be breastfeeding.

Exclusion Criteria:

1. Prior surgery for esophageal cancer;
2. Esophageal fistulae due to infiltration of the primary tumor；
3. Risk of gastrointestinal bleeding, esophageal fistula or esophageal perforation;
4. Poor nutritional status, weight loss of ≥10% in the previous 2 months, with no significant improvement after nutritional intervention;
5. Major surgery or severe trauma within 4 weeks before formal enrollment;
6. Uncontrollable pleural effusion, pericardial effusion, or ascites that requires repeated drainage;
7. Received or receiving any of the following treatments in the past:

   1. Radiotherapy or targeted therapy;
   2. Participation in a study of an investigational agent or device within 4 weeks before the first dose of study treatment;
   3. Use of systemic corticosteroids at a dose \>10 mg/day prednisone equivalent or other systemic immunosuppressive therapy within 2 weeks before formal enrollment, except for inhaled or topical corticosteroids, physiologic hormone-replacement therapy, and short-term corticosteroids used for prophylaxis or treatment of allergic reactions, nausea, or vomiting;
   4. Receipt of a live vaccine or antitumor vaccine within 4 weeks before formal enrollment;
8. Any active autoimmune disease or history of autoimmune disease (e.g., interstitial pneumonitis, uveitis, enteritis, hepatitis, pituitary gland inflammation, vasculitis, myocarditis, nephritis, hyperthyroidism, hypothyroidism); Except for patients with vitiligo or those who had asthma or allergies in childhood but did not need any intervention as adults; patients with autoimmune-mediated hypothyroidism treated with stable doses of thyroid replacement hormone and type I diabetes mellitus treated with stable doses of insulin may be included;
9. Diagnosis of immunodeficiency, including positive HIV test, other acquired/congenital immunodeficiency diseases, organ transplantation and allogeneic bone marrow transplantation;
10. Diagnosis of uncontrolled cardiac clinical symptoms or disease such as: a. NYHA II or above heart failure; b. unstable angina; c. myocardial infarction within 1 year; d. clinically significant supraventricular or ventricular arrhythmias requiring clinical intervention;
11. Severe infections (CTCAE \> grade 2), such as severe pneumonia requiring hospitalisation, bacteraemia, infectious co-morbidities, etc., within 4 weeks before formal enrollment; Baseline chest imaging suggestive of active lung inflammation, signs and symptoms of infection requiring oral or intravenous antibiotic treatment within 2 weeks before the first use of study treatment, except for prophylactic antibiotic use;
12. History of interstitial lung disease or non-infectious pneumonia, or pulmonary insufficiency ≥ grade 3 as confirmed by pulmonary function tests;
13. Active tuberculosis infection detected by history or CT examination, or history of active tuberculosis infection within 1 year before enrollment or more than 1 year previously without regular treatment;
14. Active hepatitis B infection (HBV DNA \>2000 IU/mL) or active hepatitis C infection with detectable HCV RNA;
15. Presence of abnormal sodium, potassium, and calcium laboratory test values greater than grade 1 within 2 weeks prior to enrollment that do not improve with treatment;
16. Known hypersensitivity or contraindication to camrelizumab, nab-paclitaxel, carboplatin, or any component of the protocol-defined study treatments;
17. Previously diagnosed with any other malignancy within 5 years before the first use of the investigational drug, except for malignancies with low risk of metastasis and death (5-year survival rate\>90%), such as adequately treated basal cell or squamous cell skin cancer or cervical carcinoma in situ.
18. As judged by the investigator, the subject has other factors that may lead to forced termination of the study midway.