What is malignant pheochromocytoma? How should malignant pheochromocytoma be treated? A: Various pathological indicators are used to predict the malignant behavior of pheochromocytoma, but by far the most predictive value is that pheochromocytoma located outside the adrenal gland, tumor diameter >5cm and SDHB gene mutation should be considered as malignant, in addition, blood and urine dopamine and norepinephrine levels are significantly elevated also suggest the possibility of malignancy, which needs clinical attention. The main treatments for malignant pheochromocytoma are as follows: (1) Surgery to remove the primary or metastatic lesion is still the main treatment, although surgical reduction cannot prolong survival, it can help control blood pressure and other related symptoms, and may facilitate postoperative radiotherapy or nuclear therapy. (2) Radionuclide therapy is used for those with inoperable or multiple metastases and positive MIBG or octreotide images. The most commonly used drug is 131I-MIBG, whose therapeutic effect is closely related to the absorbed dose per gram of tumor tissue and tumor volume, and the tumor diameter should be less than 2 cm to ensure good uptake of 131I-MIBG. High-dose 131I-MIBG treatment can prolong survival and relieve symptoms; the short-term effect is good, with symptom efficiency of 75%, hormone efficiency of 45%, partial remission rate of tumor volume of 30%, and complete remission rate of 5%. However, the long-term efficacy is poor, and almost all of them have recurrence or metastasis within 2 years. The main side effect is bone marrow suppression. Nuclear-labeled octreotide can be used for MIBG-negative patients, but the efficacy is difficult to evaluate. (3) Radiotherapy and chemotherapy: external radiation therapy is recommended for tumors that cannot be surgically resected and to relieve pain due to bone metastases, but may aggravate hypertension. Chemotherapy is recommended for CVD regimen (cyclophosphamide, vincristine, azelenazomib), with an efficiency of about 50%, but mostly relapses within 2 years. The combination of MIBG may improve the efficacy. Anti-angiogenic targeted drug therapy may be effective. (4) Management of catecholaminosis, alpha-blockers and beta-blockers are recommended for the control of hypertension in those with malignant or inoperable conditions.