XELOX Combined With Cadonilimab Versus XELOX as Neoadjuvant Treatment for Locally Advanced, pMMR Rectal Cancer

Inclusion Criteria: * Histologically or pathologically confirmed rectal adenocarcinoma located within 5 to 15cm from the anus with a stage of T3-4a or N+ according to the CT or endoscope * Mesorectal fascia uninvolved * Sign the informed consent form * 18 years and older * Mismatch repair proficient determined by immunohistochemistry * No prior treatment * Performance status: ECOG 0-1 * Good organ function: Blood routine: hemoglobin ≥90g/L, neutrophil ≥1.5×10\^9/L, platelet ≥100×10\^9/L; Renal function: creatinine≤1.5×upper limit of normal (UNL) or creatinine clearance ≥50ml/min; Liver function: total bilirubin (TBIL)≤1.5×upper limit of normal (UNL); ALT≤2.5×UNL, AST≤2.5×UNL; Ejection fraction at least 50% (or lower limit of normal) by echocardiogram Exclusion Criteria: * Other pathological category, such as squamous cancer * Distant metastasis or peritoneum implantation * Have received chemotherapy or radiotherapy in the past * Known to have allergic reactions to any ingredients or excipients of experimental drugs * Unable to swallow or under other circumstance which would drug absorption * Other active malignant tumors, excluding those who have been disease free for more than 5 years or in situ cancer considered to have been cured by adequate treatment * Have received colorectal cancer surgery * Diabetes was not controlled, defined as HbA1c \> 7.5% after anti-diabetic drugs or hypertension was not controlled, defined as systolic / diastolic blood pressure \> 140 / 90 mmHg after antihypertensive drug * Myocardial infarction, severe/unstable angina, New York Heart Association (NYHA) class III or IV congestive heart failure in the past 12 months * Known to be infected with human immunodeficiency virus (HIV), have acquired immunodeficiency syndrome (AIDS) related diseases, have active hepatitis B or hepatitis C * Pregnant or nursing * May increase the risk associated with participation in the study or administration of the study drug or mental illness that may interfere with the interpretation of research results * There are other serious diseases that the researchers believe patients cannot be included in the study