Neoadjuvant Tisleizumab(BGB-A317) for dMMR/MSI-H Non-late Stage CRC Patients Before Surgery

Inclusion Criteria: * Able to provide consents and agree to follow the trial requirement and assessment; * Age \>=18 * ECOG score: 0 or1 * Biopsy pathological diagnosis as MSI-H/dMMR( both IHC and PCR method required) * Measurable and assessible primary tumor sites according to RECIST 1.1 * Able to provide 22ml peripheral blood for assessment for ctDNA * With all organ function sufficient * No bowel obstruction or fistula * No previous chemotherapy, radiotherapy and immunotherapy accepted history * Distant metastasis excluded before surgery by CT scan * Contraception required for women for the whole enrollment time until 3 months after last dose of immunotherapy Exclusion Criteria: * self-autoimmune diseases history such as SLE * People who using the immune suppressor * Severe allergy to other mono-clone antibody * Cerebral metastasis which hasn't be managed yet * Hypertension(SBP\>140mmHg，DBP\>90mmHg) * Uncontrolled diabetes(FBG\>10mmol/L) * Accepted anti-PD-1 or anti-PD-L1 immunotherapy in the past * Uncontrolled heart diseases such as NYHA II heart failure, unstable angina , cardiac infarction in 1 year and arrhythmia * Systemic inflammation which needs whole body treatment * Urine routine: protein \>=++ or 24hr urine protein\>=1g * Innate or acquired immune deficiency like HIV and HBV * Enrolled in other clinical trial already * Confirmed as metastasis before the surgery * Other malignancies has been diagnosed before * Tuberculosis * Pregnancy