To explore the safety and efficacy of Surufatinib and Sintilimab in Combination With Capecitabine in Patients With Previously Treated Metastatic Adenocarcinoma of Small Intestine or Appendix Carcinoma : a Single-arm, a Single-center , Phase 2 Trial. Meanwhile, Exploring the maximum tolerant dose or recommended II research dose of Surufatinib combined with a fixed dose of Sintilimab and Capecitabine using 3 + 3 dose climbing experiment.

Inclusion Criteria:

1. Histological or cytological documentation of adenocarcinoma of Small Intestine or Appendix Carcinoma. All other histological types are excluded.
2. Subjects with metastatic adenocarcinoma of Small Intestine or Appendix Carcinoma.
3. Subjects must have failed at least one line of prior treatment.
4. Progression during or within 3 months following the last administration of approved standard therapies . 4.1 Subjects an adjuvant setting should have progressed during or within 6 months of completion of adjuvant therapy. 4.2 Subjects who have withdrawn from standard treatment due to unacceptable toxicity warranting discontinuation of treatment and precluding retreatment with the same agent prior to progression of disease will also be allowed into the study. 4.3 Subjects may have received prior treatment with Avastin (bevacizumab)
5. Subjects must have measurable or non measurable disease according to Response Evaluation Criteria in Solid Tumors (RECIST) criteria, version 1.1.
6. Eastern Cooperative Oncology Group (ECOG) Performance Status of 1.
7. Life expectancy of at least 3 months.
8. Adequate bone marrow, liver and renal function as assessed by the laboratory required by protocol.

Exclusion Criteria:

1. Prior treatment with Surufatinib
2. Previously received anti-programmed death-1 (PD-1) or its ligand (PD-L1) antibody, anti-cytotoxic T lymphocyte-associated antigen 4 (cytotoxic T- lymphocyte-associated Protein 4, CTLA-4) antibody or other drug/antibody that acts on T cell costimulation or checkpoint pathways.
3. Previous or concurrent cancer that is distinct in primary site or histology from colorectal cancer within 5 years prior to randomization EXCEPT for curatively treated cervical cancer in situ, non-melanoma skin cancer and superficial bladder tumors [Ta (non-invasive tumor), Tis (carcinoma in situ) and T1 (tumor invades lamina propria)].
4. Cardiological disease including Congestive heart failure, Unstable angina, Myocardial infarction, Cardiac arrhythmias requiring anti-arrhythmic therapy.
5. Uncontrolled hypertension. (Systolic blood pressure 150 mmHg or diastolic pressure 90 mmHg despite optimal medical management).
6. Pleural effusion or ascites that causes respiratory compromise. Arterial or venous thrombotic or embolic events.
7. Any history of or currently known brain metastases.
8. Interstitial lung disease with ongoing signs and symptoms at the time of informed consent.
9. Systemic anticancer therapy including cytotoxic therapy, signal transduction inhibitors, immunotherapy, and hormonal therapy during this trial or within 4 week.