The goal of this phase I clinical trial is to learn whether a multimodal follow-up evaluation combined with endoscopic selective neck dissection (ESND) is safe and feasible in patients with newly diagnosed N3 nasopharyngeal carcinoma.

The main questions it aims to answer are:

• Is the multimodal evaluation-guided surveillance-intervention approach safe for patients?
• Is this approach feasible for identifying and managing residual cervical lymph nodes after radiotherapy? Participants will receive standard chemoradiotherapy. After treatment, they will undergo follow-up evaluation using clinical assessment, conventional imaging, Epstein-Barr virus DNA testing, and contrast-enhanced ultrasound. Participants with clinically suspicious residual cervical lymph nodes identified by multimodal evaluation and eligible for surgery underwent endoscopic selective neck dissection.

Patients with N3 nasopharyngeal carcinoma remain at risk of residual cervical lymph nodes after radiotherapy. Conventional imaging may have difficulty distinguishing viable residual tumor from post-radiotherapy edema, fibrosis, scarring, or inflammation. Contrast-enhanced ultrasound (CEUS) provides information on lymph node microvascular perfusion and may complement routine follow-up assessment. For patients with suspected residual cervical lymph nodes, neck dissection is an established salvage treatment option. Endoscopic selective neck dissection (ESND) is a minimally invasive surgical approach based on the principles of selective neck dissection and may reduce surgical trauma. This prospective, single-center, single-arm phase I study enrolled patients with pathologically confirmed N3 nasopharyngeal carcinoma. After completion of radiotherapy, participants underwent multimodal cervical lymph node follow-up evaluation, including clinical assessment, conventional imaging, Epstein-Barr virus DNA testing, and CEUS. During follow-up, participants with suspicious residual cervical lymph nodes identified by multimodal evaluation and suitable for surgery underwent ESND. Participants were followed for adverse events, postoperative complications, disease progression, locoregional recurrence, distant metastasis, and survival outcomes. The main purpose of this study is to evaluate the safety and feasibility of this multimodal evaluation-guided surveillance-intervention strategy.

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 8th 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).

Complete de-identified patient data set will be submitted onto an online platform.