This prospective, multicenter, real-world observational study aims to evaluate whether a response-adapted individualized risk index, the RAIRI model, can identify patients with non-metastatic nasopharyngeal carcinoma who may or may not benefit from adjuvant therapy after standard chemoradiotherapy. Patients will receive standard treatment according to routine clinical practice. After completion of chemoradiotherapy and assessment at approximately 1 month after radiotherapy, longitudinal multimodal response data, including plasma cfEBV DNA dynamics and MRI-based tumor response, will be incorporated into the RAIRI model to estimate the predicted 5-year progression-free survival. Patients will be stratified into a RAIRI low-risk group, defined as predicted 5-year PFS ≥85%, and a RAIRI high-risk group, defined as predicted 5-year PFS <85%.

Within each RAIRI risk stratum, outcomes will be compared between patients who receive adjuvant systemic therapy, mainly PD-1 inhibitor-based adjuvant immunotherapy, and those who undergo routine surveillance without adjuvant systemic therapy. The primary endpoint is 3-year failure-free survival. Secondary endpoints include overall survival, locoregional relapse-free survival, distant metastasis-free survival, complete response rate after chemoradiotherapy, distribution of RAIRI risk groups, adverse events, late toxicities, and longitudinal health-related quality of life.

Nasopharyngeal carcinoma is commonly treated with intensity-modulated radiotherapy combined with platinum-based chemotherapy, with or without induction therapy. However, the optimal selection of patients for adjuvant systemic therapy after definitive chemoradiotherapy remains uncertain in routine clinical practice. Some patients may have a sufficiently favorable prognosis after chemoradiotherapy and may be safely observed, whereas others may remain at high risk of recurrence or metastasis and may benefit from treatment intensification.

This study will prospectively collect real-world clinical, imaging, laboratory, treatment exposure, toxicity, and survival data from patients with non-metastatic nasopharyngeal carcinoma treated at multiple tertiary cancer centers. The RAIRI dynamic prognostic model will be applied after completion of standard chemoradiotherapy, using baseline clinical variables and longitudinal response indicators including cfEBV DNA kinetics and MRI-based tumor regression. The model will generate an individualized predicted 5-year PFS probability. Patients with predicted 5-year PFS ≥85% will be classified as RAIRI low-risk, whereas those with predicted 5-year PFS <85% will be classified as RAIRI high-risk.

Because this is an observational study, adjuvant treatment will not be assigned by the study protocol. After chemoradiotherapy, patients may either receive adjuvant systemic therapy, mainly PD-1 monoclonal antibody therapy, or undergo routine surveillance, according to treating physician judgment and patient preference. The main analysis will compare 3-year failure-free survival between adjuvant therapy and routine surveillance within each RAIRI risk group. Propensity score matching, multivariable Cox proportional hazards models, and sensitivity analyses will be used to adjust for baseline and treatment-related confounders.

Inclusion Criteria

1. Age 18 to 75 years, male or female.
2. Histologically or cytologically confirmed EBER-positive non-keratinizing nasopharyngeal carcinoma, including differentiated or undifferentiated subtype.
3. Non-metastatic nasopharyngeal carcinoma confirmed by multimodal staging, corresponding to stage I-III according to the AJCC 9th edition staging system, or stage I-IVA according to the AJCC 8th edition staging system.
4. Eastern Cooperative Oncology Group performance status of 0-1.
5. Availability of complete pretreatment high-quality contrast-enhanced MRI of the nasopharynx and neck, including functional MRI sequences such as diffusion-weighted imaging, and at least one measurable tumor lesion according to RECIST version 1.1.
6. Availability of pretreatment quantitative plasma cfEBV DNA measurement.
7. Adequate baseline laboratory function, defined as hemoglobin >120 g/L, white blood cell count ≥4 × 10^9/L, platelet count ≥100 ×10^9/L, and liver and renal function parameters, including ALT, AST, total bilirubin, and serum creatinine, within 1.25 times the upper limit of normal; no severe clinically significant hearing impairment.
8. Ability to fully understand the nature and follow-up procedures of this observational study, and voluntary provision of written informed consent by the patient or the patient's legally authorized representative.
9. Agreement to allow the research team to use the patient's clinical data, routine diagnostic imaging data, and residual biospecimens, such as peripheral blood samples and pathological slides, for scientific research analyses.
10. Adequate major organ function, except for local compression or functional impairment directly attributable to nasopharyngeal carcinoma.
11. Good expected compliance with follow-up and reliable communication conditions, allowing completion of long-term survival follow-up.

Exclusion Criteria

1. Absence of pretreatment plasma cfEBV DNA measurement, or missing key baseline clinical variables required for RAIRI model calculation, such as age, AJCC stage, lactate dehydrogenase level, or central liquefactive necrosis status.
2. Presence of distant metastatic disease, M1.
3. History of previous or concurrent malignancy, except for non-melanoma skin cancer or cervical carcinoma in situ that has been successfully treated and has remained disease-free for more than 5 years.
4. Pregnant or breastfeeding women, or participants of reproductive potential who are unwilling to use effective contraception during the study observation period.
5. Current participation in another interventional clinical trial involving an investigational drug or medical device.
6. Severe or uncontrolled comorbidities, including myocardial infarction within the past 6 months, severe unstable arrhythmia, severe cerebrovascular accident, active gastrointestinal ulcer, uncontrolled psychiatric illness, uncontrolled diabetes mellitus, active autoimmune disease, long-term systemic immunosuppressive therapy, active severe infection requiring systemic anti-infective treatment, known history of human immunodeficiency virus infection, hepatitis B surface antigen positivity with HBV DNA >1 × 10³ copies/mL or >200 IU/mL, or hepatitis C virus antibody positivity with abnormal viral load.
7. Any personal, social, geographic, or psychiatric condition that, in the investigator's judgment, would make it impossible for the participant to complete regular follow-up visits and assessments.

Patients aged 18 to 75 years with histologically or cytologically confirmed EBER-positive, non-keratinizing, non-metastatic nasopharyngeal carcinoma who are scheduled to receive standard chemoradiotherapy with or without induction therapy in routine clinical practice. Eligible patients must have pretreatment contrast-enhanced MRI of the nasopharynx and neck, pretreatment quantitative plasma cfEBV DNA measurement, ECOG performance status of 0-1, adequate baseline organ function, and reliable follow-up conditions. After completion of chemoradiotherapy, patients may either receive adjuvant systemic therapy, mainly PD-1 inhibitor-based immunotherapy, or undergo routine surveillance according to treating physician judgment and patient preference.

Data will be available beginning 6 months following article publication.

Data will be shared with researchers whose proposed use of the data has been approved by an independent review committee identified for this purpose. Proposals should be directed to the corresponding author's email.