Multimodal Evaluation-Guided Surveillance-Intervention With Endoscopic Selective Neck Dissection for Post-Radiotherapy N3 Nasopharyngeal Carcinoma

Inclusion Criteria:

1. Aged 18 to 70 years.
2. Pathologically confirmed nasopharyngeal non-keratinizing carcinoma (differentiated or undifferentiated, i.e., WHO Type II or III).
3. Tumor staged as TanyN3M0 according to the 9th Edition of the American Joint Committee on Cancer/Union for International Cancer Control (AJCC/UICC) staging system.
4. ECOG performance status 0-1.
5. No previous neck dissection.
6. Adequate hematologic, hepatic, and renal function, defined as: white blood cell count ≥4.0 × 10\^9/L, absolute neutrophil count ≥2.0 × 10\^9/L, hemoglobin ≥90 g/L, platelet count ≥100 × 10\^9/L, aspartate aminotransferase and alanine aminotransferase ≤2.5 × the upper limit of normal, and creatinine clearance ≥60 mL/min
7. Written informed consent provided prior to study enrollment

Exclusion Criteria:

1. Ongoing receipt of other antitumor treatment or concurrent participation in another interventional clinical trial.
2. Pregnancy or breastfeeding.
3. Severe concomitant disease that may, in the investigator's judgment, pose an unacceptable risk or compromise study compliance, including severe cardiac disease, severe pulmonary dysfunction, significant renal disease, or severe psychiatric illness.
4. History of another invasive malignancy within 5 years before enrollment, except for adequately treated basal cell carcinoma of the skin, cervical carcinoma in situ, or superficial bladder tumors (Ta, Tis, or T1).