Clinical Study of Adjuvant Surufatinib Therapy for Postoperative High-risk Neuroendocrine Tumors Based on the Ninth Edition of the AJCC Staging System

Inclusion Criteria: 1. Provide written informed consent and voluntarily participate in the study. 2. Aged 18-80 years, male or female. 3. Confirmed as Stage III NET G1/G2 or any-stage NET G3 after surgical treatment. 4. Other postoperative NET patients deemed by the investigator to have high-risk factors. 5. Adequate organ function meeting the following criteria (no use of any blood components, cell growth factors, or corrective drugs within 14 days prior to the first dose of the study drug): (i) Absolute Neutrophil Count (ANC) ≥1.5×10⁹/L; (ii) Platelets ≥100×10⁹/L; (iii) Hemoglobin ≥8 g/dL; (iv) Total Bilirubin ≤1.5 × ULN; ALT and AST ≤2.5 × ULN (or ≤5 × ULN if liver metastases are present); (v) Serum Creatinine ≤1.5 × ULN or Creatinine Clearance \>60 mL/min (Cockcroft-Gault formula). 6. Female subjects of childbearing potential must have a negative serum pregnancy test within 72 hours before the first study drug dose and use effective contraception during the study and for at least 3 months after the last dose. Male subjects with female partners of childbearing potential must use effective contraception during the study and for 3 months after the last dose. Exclusion Criteria: 1. Major surgery, open biopsy, or significant trauma within 28 days prior to the first dose. 2. History of severe or poorly controlled interstitial lung disease. 3. Poorly controlled hypertension (systolic BP ≥140 mmHg or diastolic BP ≥90 mmHg) despite antihypertensive medication. 4. Poorly controlled cardiovascular diseases, including but not limited to: (i)NYHA Class II or higher heart failure; (ii) Unstable angina; (iii) Myocardial infarction within the past year; (iv) Clinically significant supraventricular or ventricular arrhythmias poorly controlled with or without intervention. 5. Significant bleeding tendency or clinically significant bleeding within 3 months prior to the first dose (e.g., gastrointestinal bleeding, hemorrhagic gastric ulcer, vasculitis). 6. Arterial/venous thrombotic events within 6 months prior to the first dose (e.g., transient ischemic attack, cerebral hemorrhage, cerebral infarction, deep vein thrombosis, pulmonary embolism). Superficial vein thrombosis may be enrolled if deemed eligible by the investigator. 7. Concurrent active malignancy requiring treatment, except for adequately treated non-melanoma skin cancer or carcinoma in situ of the cervix. 8. Pregnancy or lactation. 9. Any other condition deemed by the investigator to potentially lead to study discontinuation (e.g., severe comorbid illnesses, abnormal laboratory values, psychosocial issues).