The purpose of this study is to compare the effectiveness, safety, pharmacokinetics (PK) of SYHX2008 vs Octreotide Microspheres (Sandostatin LAR@) in patients with advanced, well-differentiated GEP-NET.

This is a Phase II, open-label randomized study to assess the PK, efficacy, and safety of SYHX2008 in adult patients with well-differentiated GEP-NET. Patients will be randomized to SYHX2008 cohort or Octreotide Microspheres cohort (Sandostatin LAR@).

Inclusion Criteria:

1. Male or female patient ≥18 years old;
2. Histologically confirmed, advanced GEP-NET;
3. At least 1 measurable, somatostatin receptor-positive lesion according to RECIST 1.1;
4. Previous treatment with ≤2 systemic antitumor drugs;
5. Patients who do not have liver metastasis, with alanine aminotransferase (ALT) and aspartate aminotransferase (AST) and alkaline phosphatase (ALP) levels ≤ 2.5 times the upper limit of normal (ULN) ; and who do have liver metastasis, with ALT and AST ≤ 5 times ULN; Serum total bilirubin <1.5 times the ULN; absolute neutrophil count (ANC) of ≥1.5×10^9/L, platelet count of ≥90×10^9/L, and hemoglobin ≥9 g/dL; or International Normalized Ratio (INR) ≤1.5 ULN and activated partial thromboplastin time (APTT) ≤1.5 ULN;
6. ECOG performance status of 0 to 1
7. Have expected survival of more than 3 months;
8. Adequately understand the study and voluntarily sign the Informed Consent Form;
9. Females patients with reproductive potential must agree to use an effective contraceptive method, for example, intrauterine devices, birth control medicine or condoms, during the study and within 3 months after study treatment discontinuation; or serum pregnancy tests negative and must be non-lactating participants; or males should agree contraception during the study and for within 3 months after study treatment discontinuation.

Exclusion Criteria:

1. Uncontrolled or severe diarrhea with significant dehydration;
2. Other malignancies diagnosed within the previous 5 years, except basal cell carcinoma or cervical carcinoma in situ after radical resection;
3. Anti-tumor therapy received within 4 weeks prior to the initiation of the investigational treatment, for example mammalian target of rapamycin (mTOR) inhibitors or multi-target tyrosine kinase inhibitors (TKI); or short-acting octreotide acetate was received subcutaneously or intravenously within 1 weeks prior to the initiation of the investigational treatment;
4. Interferon was received within 4 weeks prior to the initiation of the investigational treatment; or chemotherapy was received within 4 weeks prior to the initiation of the investigational treatment; or transarterial chemoembolization was received within 12 months prior to screening; or previously received peptide receptor radionuclide therapy (PRRT) at any time; or received radiation therapy, anti-tumor traditional Chinese medicine treatment, hepatic artery intervention embolization, liver metastasis cryoablation or radiofrequency ablation, and other systemic anti-tumor drug treatments within 4 weeks prior to the initiation of the investigational treatment; or had participated in other clinical trials within 30 days prior to screening
5. Surgery (except biopsy) within 28 days prior to the initiation of investigational treatment or unhealed surgical incision;
6. Glycated hemoglobin (HbA1c) > 8.5%;
7. Patients have symptomatic cholelithiasis or a history of symptomatic cholelithiasis at screening, but with no performed surgery treatment;
8. Patients with active brain metastases or cancerous meningitis meet any of the following criteria: a) Patients with prior brain metastases, imaging within 4 weeks prior to the first use of investigational drug show progression of the original lesion, or new brain metastases; b) Clinical symptoms associated with central nervous system metastasis did not recovery to baseline; c) Use cortisols, radiotherapy and other drugs to control the symptoms of central nervous system metastasis within 4 weeks before the first use of the investigational drug;
9. The adverse reactions of previous antitumor therapy have not returned to ≤ grade 1 according to CTCAE V5.0 (except that the investigators evaluate no safety risk, such as hair loss, grade 2 peripheral neuropathy or dysfunction);
10. Any clinically significant uncontrolled neurological, gastrointestinal, renal (serum creatinine > 1.5 ULN), pulmonary, or other significant disease requiring exclusion assessed in the opinion of the Investigator;
11. Patients had hepatitis B virus (HBV) infection with HBV DNA positive (copies ≥1×10^4/ml or ≥2000 IU/ml); known Hepatitis C antibodies positive and HCV RNA higher than the lower detection limit ; or human immunodeficiency virus (HIV) positive, treponema pallidum antibody positive;.
12. A history of allergy to any excipient of the investigational drug or any similar chemical structure to the investigational drug;
13. Patients had any severe or uncontrolled disease, including: 1) poor blood pressure control (systolic ≥160 mmHg or diastolic ≥100 mmHg);2) grade I or higher myocardial ischemia or myocardial infarction, symptomatic or poorly controlled arrhythmia, or congenital long QT syndrome (including QTcF ≥450ms for males, QTcF ≥470ms for females), or ≥ Grade 2 congestive heart failure [NYHA classification]; 3) serious infections that are not under control (oral or intravenous systemic anti-infection therapy is required for 2 weeks before the first use of the investigational drug, except for uncomplicated urinary tract infections and upper respiratory tract infections);4) previous or current severe bleeding (>30ml of bleeding within 3 months), hemoptysis (>5ml of fresh blood within 4 weeks), or thromboembolic events (including transient ischemic attacks) within 12 months;
14. Other disease, metabolic disorder, physical examination anomaly, abnormal laboratory result, or any other conditions are inappropriate for the use of the investigational product or affect interpretation of study results.