• With a full understanding of the study, each participant volunteered to participate in this study and signed the informed consent (ICF) with good compliance and follow-up.

• Age ≥18 and ≤70.

• ECOG physical status score is 0 or 1.

• Expected survival period ≥ 12 weeks.

• Patients with histopathological confirmed MSS/pMMR-type adenocarcinoma of the colon and upper rectum which is not amenable to radiotherapy.

• R0 resection was expected to be achieved by necessarily combined organ resection, or R0 resection cannot be achieved, assessed by CT and/or MRI and multidisciplinary team (MDT) discussion.

• The clinical stage was cT4N1-2M0 or cT4bN0M0 according to AJCC 8th edition.

• Patients with multiple primary colorectal cancer are eligible, if one of the primary tumors meets the inclusion criteria.

• Patients with intestinal obstruction was relieved by colonic stenting or ostomy.

⁃ Patients had not received systematic therapy, such as surgery, chemotherapy, radiotherapy, targeted therapy, or immunotherapy.

⁃ At least one evaluable lesion (according to RECIST v1.1 standard);

⁃ Adequate organ function according to the following laboratory test values:

∙ Hemoglobin value ≥90g/L.

‣ White blood cell count ≥3.5\*109/L.

‣ Absolute neutrophil count ≥1.5\*109/L.

‣ Platelet count ≥100\*109/L.

‣ Serum creatinine ≤ upper limit of normal (ULN) or creatinine clearance ≥60ml/min.

‣ Total serum bilirubin ≤1.5 upper normal limit (ULN).

‣ Aspartate aminotransferase (AST/SGOT) and alanine aminotransferase (ALT/SGPT) ≤2.5 upper limit of normal value (ULN).

⁃ Women with reproductive potential (\< 2 years after the last menstrual period) and men use effective contraceptive methods until half a year after the last treatment.