Surgery Plus Postoperative Radiotherapy for T4 Sinonasal Adenoid Cystic Carcinoma: A Prospective Observational Study

Inclusion Criteria: 1. Age 18 80 years, any gender; ECOG performance status 0 2; life expectancy ≥6 months. 2. Histologically confirmed primary sinonasal adenoid cystic carcinoma (cribriform, tubular, solid, or mixed type). Other malignancies excluded. 3. T4 stage (T4a or T4b) according to AJCC 8th edition, based on contrast enhanced MRI/CT. 4. N0 2 (operable lymph node metastasis allowed). 5. M0 (no distant metastasis on chest CT and abdominal ultrasound) OR M1 with stable limited lung metastases; (c) stable on two CT scans ≥3 months apart; (d) no respiratory symptoms. 6. Previously untreated (no radiotherapy, chemotherapy, targeted therapy, immunotherapy, or tumor resection). MDT deems technically resectable (R0/R1 achievable, not diffusely unresectable). 7. Adequate organ function within 14 days before enrollment: ANC ≥1.5×10⁹/L, platelets ≥100×10⁹/L, Hb ≥90 g/L; ALT/AST ≤2.5×ULN, TBil ≤1.5×ULN, Cr ≤1.5×ULN or CrCl ≥50 mL/min; LVEF ≥50%, no uncontrolled arrhythmia. 8. Willing and able to provide written informed consent for clinical data collection (and optional biospecimen banking). Investigator judges good compliance. Exclusion Criteria: 1. Progressive lung metastases within 6 months (new lesions or \>20% increase); extrapulmonary metastases (liver, bone, brain); symptomatic lung metastases. 2. MDT judged unresectable, e.g., bilateral cavernous sinus invasion, brain parenchyma invasion, bilateral internal carotid artery encasement. 3. Primary tumor outside sinonasal cavity (e.g., major salivary glands, oropharynx); non ACC histology. 4. Other active malignancy within 5 years (except cured basal cell carcinoma, cervical carcinoma in situ, etc.). 5. Severe comorbidities: NYHA class III/IV heart failure, recent myocardial infarction or unstable angina, uncontrolled hypertension (≥160/100 mmHg); COPD requiring home oxygen or interstitial lung disease; decompensated cirrhosis; active hepatitis B/C without antiviral therapy; nephropathy requiring dialysis; active serious infection; active bleeding or coagulopathy (INR \>1.5×ULN without anticoagulation, or platelets \<50×10⁹/L). 6. Special populations: pregnant or breastfeeding; unwilling to use contraception (if childbearing potential); severe allergy to medications required for surgery/radiotherapy; severe psychiatric or cognitive disorder impairing cooperation; currently participating in another interventional trial. 7. Unable to undergo contrast enhanced MRI (metal implants, claustrophobia, gadolinium allergy); investigator judges inability to complete follow up (e.g., living abroad, substance abuse).