The Safety and Tolerability of PD-L1 Monoclonal Antibody Plus Lenalidomide in The Treatment of Colorectal Cancer

Inclusion Criteria: 1. Aigned informed consent 2. Only patients aged 18-75 years were enrolled 3. Patients with advanced colorectal cancer diagnosed by pathology and imaging.Note: the presence of distant metastases should be confirmed by a CT or MR scan.Bone scan should be performed if bone metastases are suspected.Local radiotherapy for pain relief is permitted for bone metastases. 4. Measurable lesions based on Response Evaluation Criteria In Solid Tumors (RECIST) 1.1 must be present.Local radiotherapy of target lesions is not allowed. 5. pMMR/MSS advanced colorectal cancer patients with disease progression or intolerance to third-line treatment after failure of current standard third-line treatment 6. ECOG 1 minute or less 7. Tumor specimens that can be used to detect the status of pd-l1, MSI, b-raf and k-ras can be provided.This test requires the patient to provide paraffin embedded biopsy specimens or white slices. 8. White blood cells ≥ 4×109/L, platelets ≥ 100×109/L without transfusion, neutrophil absolute value (ANC) ≥ 1.5×109/L without treatment with granulocyte stimulating factor, and hemoglobin ≥ 90 g/L. 9. Bilirubin ≤ 1.5 times of the upper limit of normal value, and cereal grass and cereal propyl transaminase ≤ 2.5 times of the upper limit of normal value. 10. Serum creatinine ≤ 1.5 times the upper limit of normal value, or GFR\>45 ml/min 11. Serum albumin ≥ 25 g/L (2.5g /dL) 12. INR or APTT ≤ 1.5 times ULN 13. Hepatitis B/C surface antigen positive patients need to be tested for Hepatitis B /C virus DNA quantitative test, only \< the upper limit of the normal detection value can be included in the group, and long-term use of anti-hb/hc drugs 14. Drug elution time: 28 days or 5 half-lives from the last drug application. Exclusion Criteria: 1. Allergy to any experimental drug or its excipients, or history of severe allergy, or contraindication to the experimental drug 2. Having a history of autoimmune disease or being active 3. Previous allogeneic bone marrow transplantation or organ transplantation 4. Congenital pulmonary fibrosis, drug-induced pneumonia, organized pneumonia, or ct-confirmed active pneumonia 5. HIV positive 6. Active Hepatitis B /C(Hepatitis B /C viruses have higher quantification than normal) 7. Active stage tuberculosis 8. Uncontrolled cancer pain 9. A live attenuated vaccine was injected within 4 weeks before the study began, or a live attenuated vaccine is expected to be injected during the trial or within 5 months after the end of the trial 10. Previous use of immunotherapy, including CTLA4, anti-PD-1, or anti-PD-L1 monoclonal antibody 11. CT indicates lung active inflammation 12. Systemic administration of glucocorticoids or immunosuppressants within 2 weeks prior to the trial.Inhaled corticosteroids and halocorticoids are allowed 13. Use of hormones is contraindicated 14. Serious cardiovascular disease, myocardial infection, arteriovenous thrombosis or cerebrovascular accident, arrhythmia, unstable angina pectoris within 3 months before the trial 15. Uncontrollable increase in blood pressure or blood sugar 16. History of other malignancies 5 years ago, except for carcinoma in situ of the cervix, non-melanoma skin cancer or stage I uterine cancer 17. Peripheral neuropathy of grade 2 ≥ NCI CTCAE 18. Serum albumin less than 2.5g /dL 19. Uncontrolled or symptomatic hypercalcemia 20. Infection requiring antibiotics within 14 days prior to trial 21. Chronic enteritis 22. Clinically significant active gastrointestinal bleeding 23. Non-diagnostic surgery within 4 weeks before the trial 24. Any other disease for which there is evidence that the use of the experimental drug needs to be restricted 25. Participate in other trials within 30 days prior to the trial or plan to participate in other trials during the trial 26. Receive other experimental drugs within 28 days before the start of the trial 27. Women who are pregnant or lactating, or who plan to become pregnant within 5 months after the end of treatment.Women of childbearing age should undergo a blood pregnancy test 7 days before the start of the trial 28. Use of PD-L1 monoclonal antibody or lenalidomide contraindications 29. MSI-H/dMMR in patients with advanced colorectal cancer