The purpose of this study is to evaluate the efficacy and safety of sintilimab and chidamide in combination with or without IBI305(bevacizumab) in patients with standard treatment failure of advanced or metastatic pMMR/MSS colorectal adenocarcinoma.

In this study, we explored the potential effectiveness of combining PD-1 monoclonal antibody sintilimab with the histone deacetylase inhibitor (HDACi) chidamide, with or without IBI305(bevacizumab), in MSS/pMMR unresectable locally advanced or metastatic colorectal cancer patients who failed standard chemotherapy and testified this new combination in preclinical models. Fourty-eight patients were randomized into two groups: the doublet group, who received sintilimab 200 mg every 3 weeks and chidamide 30 mg orally twice weekly, and the triplet group, who received sintilimab, chidamide, and bevacizumab 7.5 mg/kg every 3 weeks.

Inclusion Criteria:

1. Histologically confirmed diagnosis of unresectable locally advanced, recurrent or metastatic colorectal adenocarcinoma.
2. Tumor tissues were identified as mismatch repair-proficient (pMMR) by immunohistochemistry (IHC) method or microsatellite stability (MSS) by polymerase chain reaction (PCR).
3. Subjects must have failed at least two lines of prior treatment.
4. Subjects must have one measurable lesion according to RECIST v1.1 at least.
5. Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1.
6. 18-75 years old.
7. Life expectancy of at least 12 weeks.
8. Adequate bone marrow, liver, renal and coagulation function as assessed by the laboratory required by protocol

Exclusion Criteria:

1. Previously received anti-programmed death-1 (PD-1) or its ligand (PD-L1) antibody or histone deacetylase (HDAC) inhibitor.
2. Received last dose of anti-tumor therapy (chemotherapy, targeted therapy, tumor immunotherapy or arterial embolization) within 3 weeks of the first dose of study medication.
3. Received radiotherapy with 4 weeks of the first dose of study medication.
4. Underwent major operation within 4 weeks of the first dose of study medication or open wound, ulcer or fracture.
5. Known symptomatic central nervous system (CNS) metastasis and/or carcinomatous meningitis. Subjects received prior treatment and have stable disease more than 4 weeks from first dose of study medication are permitted to enroll.
6. Active, known or suspected autoimmune disease or has a history of the disease within the last 2 years.
7. Interstitial lung disease requiring corticosteroids.
8. Active or poorly controlled serious infections.
9. Significant malnutrition.
10. Symptomatic congestive heart failure (NYHA Class II-IV) or symptomatic or poorly controlled arrhythmia.
11. Uncontrolled hypertension (systolic blood pressure ≥ 150 mmHg or diastolic blood pressure ≥ 100 mmHg) despite standard treatment.
12. Within 6 months prior to the enrollment, history of gastrointestinal perforation and/or fistula, gastrointestinal ulcer, bowel obstruction, extensive bowel resection, Crohn's disease, or ulcerative colitis, intra-abdominal abscesses, or long-term chronic diarrhea.
13. History or evidence of inherited bleeding diathesis or coagulopathy or thrombus
14. Any life-threatening bleeding within 3 months prior to the enrollment.
15. High risk of bleeding.