Treatment principles Internal treatment is divided into two parts: symptom control and anti-proliferation. Symptom control is mainly symptomatic treatment to relieve the symptoms caused by tumor hormone secretion; while anti-proliferative treatment mainly includes biological therapy, targeted drug therapy and chemotherapy. For G1/G2 patients, drugs should be selected according to the size and aggressiveness of their tumor load, and for slow-growing tumors with small load, they can even choose to wait for observation. For G3 patients, chemotherapy-based treatment should be actively adopted. In conclusion, individualized treatment plan should be formulated by integrating the primary focus, metastatic site and the above characteristics. Specific regimen Symptom control Symptom control can be preferred to growth inhibitor analogs (SSA) and interferon biotherapy. In addition, for different hormone types secreted by tumors, appropriate antagonists can be considered to inhibit their secretion. For example, proton pump inhibitor (PPI) can be used to inhibit gastric acid secretion in gastrinoma, adrenal blockers such as ketoconazole or methylphenidate can be chosen for Cushing’s syndrome caused by adrenocorticotropic hormone (ACTH) tumor, diazoxide can be used to control insulin secretion in insulinoma, and verapamil, phenytoin and glucocorticoids can also be chosen. Besides, local treatment (such as liver intervention or radiofrequency treatment) can also achieve better symptom control. Anti-proliferative Anti-proliferative drugs include biological therapy drugs, targeted drugs and chemotherapy drugs. The pathological grading of the tumor should be clarified before treatment. For G1/G2 patients, if the tumor load is relatively small and the growth is slow, growth inhibitor analogue (SSA) therapy can be considered. If the tumor load is large or growing very rapidly, chemotherapy should be considered first, while targeted drug therapy can be considered for cases in between (Figure 1). For G3 patients, chemotherapy should be the mainstay, with etoposide, irinotecan, platinum, temozolomide, fluorouracil, and bevacizumab being the drugs of choice. Combination SSA therapy may also be considered for patients with positive octreotide imaging. Biologic therapy As mentioned earlier, biologic therapy includes SSA and interferon α. SSA mainly includes octreotide acetate microspheres and lanreotide. SSA can be used in all GEP-NETs and is characterized by low side effects, well tolerated by patients, and can be used in patients with poor general condition, poor organ function or advanced age; and can be considered to increase the dose or shorten the duration of dosing when the tumor tends to progress. For some patients, it can still achieve the effect of continuing to control tumor growth. Interferon is currently not used much in China and can be used alone or in combination with octreotide, but is usually used in second-line therapy and beyond. Biologic therapies are generally less effective (<10%), but are better tolerated by patients. < p=""> Chemotherapy has been used mainly for pNET, metastatic foregut NET, and NEC, while the efficacy for midgut NET remains to be further investigated. For pNET, a regimen of urethromycin ± fluorouracil is preferred abroad. Since this drug is not yet available in China, the common regimen for G2NET in China is temozolomide±capecitabine, and this regimen is not yet supported by large-scale clinical studies, but several studies in small samples have confirmed that this regimen can achieve high tumor remission rates (up to 70%) and progression-free survival (PFS) of up to 18 months, especially for pNET patients. There are no validated markers to screen patients for temozolomide ± capecitabine, and this regimen may be attempted for GI-NET where standard therapy has failed. A platinum-based regimen [EP: pegylated glycosides + cisplatin, IP: irinotecan + cisplatin] is recommended for first-line treatment of NEC, while temozolomide + capecitabine ± bevacizumab can be considered for second-line treatment. In addition, irinotecan and oxaliplatin-based regimens can be tried. Targeted therapies Targeted drugs include sunitinib and everolimus, which are currently approved only for pNET. both have large phase III clinical studies confirming their efficacy, with PFS close to 1 year for both drugs. Although the efficiency of targeted drugs did not exceed 10%, the proportion of tumor shrinkage after treatment was significantly higher than that of the placebo group. The use of RECIST for targeted drug efficacy evaluation is still controversial, and a more scientific evaluation system is expected to be introduced in the future. For GI-NET that failed standard treatment, the regimen of everolimus ± SSA can be considered.