Inclusion Criteria:
1. Aged 14 to 85 years.
2. Adrenal pheochromocytoma or retroperitoneal paraganglioma suspected based on imaging and biochemical diagnoses.
3. Scheduled for surgical treatment.
4. American Society of Anesthesiologists (ASA) physical status classification of Grade Ⅰ to Ⅲ.
5. Informed consent obtained from the patient or their legal guardian.
6. Confirmed non-pregnant and non-lactating status.
7. Laboratory requirements:
* Absolute Granulocyte Count (AGC) \> 1.5 × 10⁹/L;
* Platelet count \> 80 × 10⁹/L;
* Hemoglobin (Hb) \> 90 g/L;
* Serum bilirubin \< 1.5 × the upper limit of normal (ULN);
* Serum creatinine \< 1.5 × ULN or creatinine clearance \>= 60 mL/min;
* Negative serum human chorionic gonadotropin (hCG) test result.
8. Capacity to understand the study and willingness to sign a written informed consent form.
Exclusion Criteria:
1. Incapable of correctly understanding the content of questionnaires and unable to cooperate with researchers.
2. Receiving other anti-tumor drug therapies.
3. Pregnant or lactating women, and men or women of childbearing age who refuse to take appropriate contraceptive measures.
4. A history of allergic reactions to belzutifan or hypoxia-inducible factor (HIF) inhibitors.
5. Presence of multiple factors affecting oral drug administration (e.g., dysphagia, chronic diarrhea, intestinal obstruction, etc.) or other conditions interfering with medication intake.
6. Severe myelosuppression or coagulation abnormalities (International Normalized Ratio (INR) \> 1.5, or Prothrombin Time (PT) \> upper limit of normal (ULN) by 4 seconds, or Activated Partial Thromboplastin Time (APTT) \> 1.5 × ULN), a bleeding tendency, or ongoing thrombolytic or anticoagulant therapy.
7. A history of treatment with other HIF inhibitors.
8. Prior receipt of chemotherapy, targeted therapy, biological agents, or other investigational treatments within the 4 weeks prior to the first administration of the study intervention.
9. Active or uncontrolled comorbid diseases, including but not limited to:
* Uncontrolled myocardial ischemia or myocardial infarction, cardiac arrhythmias (including corrected QT interval (QTc) \>= 480 ms), and uncontrolled congestive heart failure of New York Heart Association (NYHA) Grade \>= 2;
* Clinically significant heart disease, including unstable angina pectoris, acute myocardial infarction, or a history of Coronary Artery Bypass Grafting (CABG) or Percutaneous Transluminal Coronary Angioplasty (PTCA) within 6 months prior to study enrollment, or congestive heart failure of NYHA Grade Ⅲ or Ⅳ;
* Persistent or active infection;
* Liver cirrhosis, decompensated liver disease, active hepatitis, or chronic hepatitis requiring antiviral therapy;
* Renal failure requiring hemodialysis or peritoneal dialysis;
* A history of immunodeficiency, including Human Immunodeficiency Virus (HIV) infection or other acquired/congenital immunodeficiency diseases, or a history of organ transplantation.
10. A history of seizures requiring medical treatment.
11. Occurrence of any of the following conditions within 6 months prior to study registration: Cerebrovascular Accident (CVA) or Transient Ischemic Attack (TIA); severe or unstable cardiac arrhythmia; pulmonary embolism or untreated Deep Venous Thrombosis (DVT).
12. A history of psychoactive substance abuse with inability to abstain, or presence of mental disorders.
13. Concomitant use of drugs that interact with belzutifan.
14. Patients with stable disease who decline surgical treatment.
15. Resting pulse oximetry reading \< 92%, or requirement for intermittent oxygen supplementation, or long-term oxygen therapy.
