Phase II Clinical Study of Leflunomide in the Treatment of MEN-1 Neuroendocrine Tumor

Inclusion Criteria: * Age 18-75 years, gender unlimited * Pathological diagnosis of neuroendocrine tumor * MEN-1 germ line mutation (MEN-1 syndrome), or tumor with somatic MEN-1 mutation * Unresectable neuroendocrine tumors that have failed standard first-line systemic therapy * At least one evaluable lesion according to the RECIST criteria * ECOG physical condition score: 0-1 * Voluntarily joined the study, signed the informed consent, complied well, and cooperated with the follow-up. * Must meet the following requirements: Bone marrow: leukocyte \> 4.0×109/L, neutrophils ≥1.5×109/L, platelets ≥100×109/L, hemoglobin ≥10g/dL; Liver: total bilirubin \< 1.5 times the upper limit of normal, AST/ALT≤1.5 times the upper limit of normal value, Lactate dehydrogenase ≤1.5 times the upper limit of normal value, Alkaline phosphatase ≤5 times the upper limit of normal value; Kidney: serum creatinine ≤1.5 times the upper limit of normal value or creatinine clearance ≥60ml/min Exclusion Criteria: * Received any antitumor therapy within 4 weeks * Participated in or are participating in clinical trials of other drugs/therapies within 4 weeks prior to the initial use of the study drug * Underwent/received major surgery or has not recovered from the side effects of the surgery within 4 weeks prior to the initial use of the study drug * Subjects of other malignant tumors unless complete remission was achieved at least 2 years prior to study inclusion and not required other treatment during the study period * Persistent or active (serious) infection * Hypertension that is difficult to control with medication (continuous blood pressure is greater than 150/90 MMHG * Poorly controlled diabetes * Grade II/IV congestive heart failure or heart block * Within 6 months prior to use for the first time seen in the following situations: Deep vein thrombosis; Pulmonary embolism; Myocardial infarction; Serious arrhythmia; Instability or angina pectoris; Percutaneous coronary intervention; Acute coronary syndrome; Coronary artery bypass grafting * Be allergic to leflunomide tablets and their metabolites * Severe liver damage * Other severe acute or chronic medical conditions or abnormalities in laboratory tests that may increase the risks associated with study participation or may interfere with the interpretation of study results * Poor compliance, or other conditions unsuitable for participation in this trial