Inclusion Criteria:
1. This study has been fully understood and voluntarily signed informed consent ;
2. Age 18-75 years old ( including 18 and 75 years old ) ; rectal adenocarcinoma was histologically confirmed as pMMR / MSS type ( according to the detection criteria of the institutional testing center, it can be detected by immunohistochemistry, PCR or NGS ), and was staged as stage II ( T3-4N0 ) or stage III ( T1-4N1-2 ) by MRI and CT.
4.MRI was used to evaluate the middle and low rectal cancer below 10 cm from the anal margin of the tumor ; 5.Patients who were recommended for neoadjuvant therapy after evaluation by the Multidisciplinary Oncology Committee ; 6.ECOG physical condition 0-1 points ; 7.Expected survival ≥ 2 years ; 8.No previous anti-tumor treatment has been received ; the function of vital organs meets the following requirements ( not allowed to use any blood components and cell growth factors within \* 14 days before enrollment ) : Absolute neutrophil count ≥ 1.5 × 109 / L ; platelet ≥ 100 × 109 / L ; hemoglobin ≥ 90g / L ; total bilirubin \< 1.5 times ULN ; aLT and / or AST \< 2.5 times ULN ; serum creatinine \< 1.5 times ULN ; endogenous creatinine clearance rate ≥ 50ml / min ; 10. Women of childbearing age need to take effective contraceptive measures ; 11.good compliance, with follow-up.
Exclusion Criteria:
* 1.Unable to comply with the research program or research procedures ; 2.Patients with surgical taboos ; 3.Patients with metastatic disease or recurrent rectal cancer ; 4.Patients with familial adenomatous polyposis ( FAP ), hereditary nonpolyposis colorectal cancer ( HNPCC ), active Crohn 's disease or active ulcerative colitis ; 5.Patients with other malignant tumors within 5 years before enrollment, except for basal cell or squamous cell carcinoma of the skin after radical resection, or cervical carcinoma in situ ; 6.Severe cardiovascular diseases, including unstable angina or myocardial infarction, occurred within 6 months before enrollment ; 7.Subjects who were allergic to the study drug or any of its adjuvants ; 8.Participated in other domestic unapproved or unlisted drug clinical trials within 4 weeks before enrollment and received corresponding experimental drug treatment ; 9.International normalized ratio ( INR ) \> 1.5 or activated partial thromboplastin time ( APTT ) \> 1.5 × ULN ; 10.Investigators judged clinically significant electrolyte abnormalities ; 11.There was uncontrolled hypertension before enrollment, which was defined as : systolic blood pressure ≥ 140 mmHg and / or diastolic blood pressure ≥ 90 mmHg ; 12.There were poorly controlled diabetes before enrollment ( after regular treatment, fasting glucose concentration ≥ CTCAE grade 2 ) ; 1.3.13.Before enrollment, there are any diseases or states that affect drug absorption, or patients cannot take oral drugs ; 14.Before entering the group, there were gastrointestinal diseases such as gastric and duodenal active ulcers and ulcerative colitis, or other conditions that may cause gastrointestinal bleeding and perforation determined by the researchers ; 15.Severe active bleeding, hemoptysis ( fresh blood \> 5 mL within 4 weeks ) or thromboembolic events occurred within 12 months before enrollment ( package ).
