Although immunotherapy combined with chemotherapy has become the first-line standard regimen for advanced esophageal squamous cell carcinoma (ESCC) and improved clinical outcomes in advanced patients, the prognosis of patients with esophageal cancer remains unsatisfactory, with a 5-year overall survival rate below 20%. As an effective modality for local disease control, local radiotherapy has no established optimal sequencing schedule when combined with systemic therapy. The timing of radiotherapy intervention may directly affect treatment efficacy, treatment tolerance and quality of life of patients.

Several studies have explored the impact of radiotherapy timing in oligometastatic ESCC, yet substantial limitations persist in current evidence, resulting in a lack of unified guideline recommendations and wide heterogeneity in clinical practice. Most existing investigations are retrospective or small-sample prospective studies with high heterogeneity in study design, patient population selection and treatment regimens, yielding inconsistent conclusions that cannot support consistent clinical consensus.

To clarify the impact of radiotherapy timing on clinical efficacy in oligometastatic esophageal cancer, the investigator designed the present clinical trial. This study aims to compare the efficacy and safety of concurrent radiotherapy versus sequential radiotherapy on the basis of immunochemotherapy among patients with oligometastatic ESCC, so as to fill the evidence gap in existing research.

Inclusion Criteria:

1. An eastern cooperative oncology group (ECOG) score of 0-1.
2. Histologically or cytologically confirmed diagnosis of esophageal squamous cell carcinoma.
3. Genuine oligometastasis (without a history of polyme-tastatic disease).
4. A total of four or fewer distant metastases, a maximum of three metastases in a single organ, and a maximum diameter of each metastatic lesion not exceeding 5 cm.
5. Biopsy of a metastatic lesion, PET/CT scan, and PD-L1 CPS (IHC 22C3) are not required but preferred.
6. No history of anti-PD-1/PD-L1 therapy. However, the following conditions are also eligible for inclusion: the use of anti-PD1/PD-L1 during induction/neoadjuvant/ concurrent therapy, or the use of anti-PD1/PD-L1 for maintenance therapy but not due to toxicity or disease progression interrupting anti-PD1/PD-L1 treatment, and the interruption has lasted for more than 3 months.
7. Adequate hematological, hepatic, renal, and coagula-tion function. Baseline laboratory tests required to assess eligibility, including ANC ≥ 1.5 × 10^9/L, PLT ≥ 80 × 10^9/L, Hb ≥85 g/L, ALB ≥28 g/L, TBIL ≤ 1.5 × ULN, ALT and AST ≤ 3 × ULN, Cr ≤ 1.5 × ULN or CrCl ≥40 mL/min, FEV1 ≥ 1 L. (liver metastases ALT and AST ≤ 5 × ULN, liver or bone metastases AKP ≤ 5 × ULN).(9) Enrolled voluntarily and signed informed consent by the patient himself or his legal representative.

Exclusion Criteria:

1. Pregnant or lactating women.

2. Lung V20 remains over 25%.

3. Confirmed diagnosis or clinical suspicion of esophageal fistula.

4. Recurrence in the irradiated field.

5. Active infection requiring systemic therapy.

6. Active autoimmune disease requiring systemic treat-ment in the past 2 years.

7. Immunodeficiency diagnosis, systemic steroid therapy, or any immunosuppressive treatment within 7 days before the first study treatment dose.

8. Patients with a known history of grade 3 or higher adverse events, which are unsuitable for Anti-PD-1 therapy or adverse events that have not recovered to ≤CTCAE grade 1 (except alopecia).

9. Uncontrolled pleural effusion, pericardial effusion, or pelvic ascites requiring repeated drainage.

10. Unable or rejection to receive Anti-PD-1 therapy or unable to comply with study requirements or follow-up schedule.(11) Inability to provide informed consent.

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Oligometastatic ESCC