This is a multi-center, open-label, phase Ib study evaluating safety and efficacy of the humanized anti-PD-1 antibody JS001, as a monotherapy in patients with neuroendocrine tumors who have failed in previous systemic treatment. 40 patients are enrolled and injected with the humanized anti-PD-1 antibody 3mg/mg every 2 weeks until disease progresses or unacceptable toxicity.

Inclusion Criteria:

1. Must have read, understood, and provided written informed consent voluntarily. Willing to adhere to the study visit schedule and the prohibitions and restrictions specified in this protocol.

2. Male and Female aged 18 and older are eligible;

3. Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1;

4. Histologic diagnosis of locally advanced or metastatic nonfunctional neuroendocrine tumors, including well-differentiated neuroendocrine tumors and pooly-differentiated neuroendocrine carcinoma;

5. Ki-67 index ≥10%;

6. Unresectable;

7. Radiographic evidence of disease rogression by RECIST criteria on or after last anti-cancer therapy within 6 months;

8. Prior treatment meeting the following criteria:

   • Patients with pooly-differentiated neuroendocrine carcinomas must have received platinum based lineds of chemotherapy;
   • Patients with well-differentiated neuroendocrine tumors must have received at least one systemic treatment, including somatostatin analogs, mTOR inhibitors, anti-angiogentic agents and chemotherapy;

9. Providing with tumor specimen (for testing the expression of PD L1 and the infiltrating lymphocytes);

10. Predicted survival >=3 months;

11. At least 1 measurable lesion (only 1 measurable lymph node lesion is excluded) (routine CT scan >=20mm, spiral CT scan >=10mm, no prior radiation to measurable lesions);

12. Screening laboratory values must meet the following criteria (within past 14 days): hemoglobin ≥ 9.0 g/dL; neutrophils ≥ 1500 cells/ μL; platelets ≥ 100 x 10^3/ μL; total bilirubin ≤ 1.5 x upper limit of normal (ULN); aspartic transaminase (AST) and alanine transaminase (ALT) ≤ 2.5 x ULN without, and ≤ 5 x ULN with hepatic metastasis; serum creatinine ≤1╳ULN, creatinine clearance >50ml/min (CockcroftGault equation) PT/INR, aPTT≤1.5 x ULN;

13. Without systemic steroids within past 4 weeks;

14. Brain or meningeal metastases must be disposed with surgery or radiation, and be stable clinically for at least 3 months (prior systemic steroids was allowed, but concurrent administration of systemic steroids with the study drug is excluded);

15. Males or female of childbearing potential must: agree to use using a reliable form of contraception (eg, oral contraceptives, intrauterine device, control sex desire, double barrier method of condom and spermicidal) during the treatment period and for at least 12 months after the last dose of study drug.

Exclusion Criteria:

1. Prior treatment with antiPD1/PDL1/PDL2 antibody;
2. Hypersensitivity to recombinant humanized antiPD1 monoclonal Ab or its components;
3. Prior treatment with mAb within past 4 weeks;
4. Prior antitumor therapy (including corticosteroids and immunotherapy) or participation in other clinical trials within past 4 weeks, or have not recovered from toxicities since the last treatment;
5. Pregnant or nursing;
6. Positive tests for HIV, HCV, HBsAg or HBcAb with positive test for HBV DNA (>500IU/ml);
7. History with tuberculosis;
8. Patients with any active autoimmune disease or a documented history of autoimmune disease, or history of syndrome that required systemic steroids or immunosuppressive medications, such as hypophysitis, pneumonia, colitis, hepatitis, nephritis, hyperthyroidism or hypothyroidism;
9. Severe, uncontrolled medical condition that would affect patients' compliance or obscure the interpretation of toxicity determination or adverse events, including active severe infection, uncontrolled diabetes, angiocardiopathy (heart failure > class II NYHA, heart block >II grade, myocardial infarction, unstable arrhythmia or unstable angina within past 6 months, cerebral infarction within past 3 months) or pulmonary disease ( interstitial pneumonia, obstructive pulmonary disease or symptomatic bronchospasm);
10. Evidence with active CNS disease;
11. Meningeal carcinomatosis;
12. Prior treatment with bone marrow stimulating factors，such as CSF (colony stimulating factor), EPO (erythropoietin), within past 2 weeks;
13. Prior live vaccine therapy within past 4 weeks;
14. Prior major surgery within past 4 weeks (diagnostic surgery excluded);
15. Psychiatric medicines abuse without withdrawal, or history of psychiatric illness;
16. Prior malignancy active within the previous 5 years except for locally curable cancers that have been apparently cured, such as basal cell skin cancer or carcinoma in situ of the cervix;
17. Underlying medical condition that, in the Investigator's opinion, would increase the risks of study drug administration or obscure the interpretation of toxicity determination or adverse events.