The Efficacy of Watch and Wait Strategy or Surgery After Neoadjuvant Immunotherapy for Locally Advanced Colorectal Cancer With dMMR/MSI-H Guided by MRD Dynamic Monitoring: A Single-center, Open-label, Prospective, Phase II Clinical Trial.

Exclusion Criteria1

• Immunohistochemistry of tumor biopsy specimens suggested pMMR or microsatellite instability detection suggested MSS ; 2. Chronic hepatitis B or C ( high-copy viral DNA ) with a history of HIV infection or active phase ; 3.Autoimmune diseases ; 4.Other active clinical severe infections ( \> NCI-CTC3.0 version ) ; 5. patients with clinical stage I ; 6.Preoperative evidence of distant metastasis ; 7. cachexia, organ dysfunction ; 8. Have a history of pelvic or abdominal radiotherapy ; 9. Patients whose seizures require treatment ( e.g. steroids or antiepileptic treatment ) ; 10.5 years have a history of other malignant tumors, except for cured cervical carcinoma in situ or skin basal cell carcinoma ; 11. Chronic inflammatory bowel disease, intestinal obstruction ; 12. Drug abuse and medical, psychological or social conditions may interfere with patient participation in the study or have an impact on the evaluation of the results of the study ; 13.Known or suspected allergies to the study drug or any drug related to this test ; any unstable condition or condition that may endanger patient safety and compliance ;