Sintilimab Combined With LCCRT Followed by Capeox Chemotherapy in pMMR/MSS/MSI-L Locally Advanced Rectal Cancer

Inclusion Criteria

1. Has signed the written Informed Consent Form and is capable of complying with the visit schedules and relevant procedures specified in the protocol.
2. Histopathologically confirmed locally advanced rectal adenocarcinoma, with clinical stage cT3-4NanyM0 or cT1-2N1-2M0 as defined by the AJCC 8th edition, and assessed as amenable to R0 resection after neoadjuvant therapy. MRI demonstrates that the lower edge of the tumor is within 10 cm from the anal verge.
3. Tumor pathological tissue testing confirms pMMR, i.e., immunohistochemical staining shows positive expression of all four proteins MLH1, MSH2, MSH6, and PMS2, or tumor tissue-based genetic testing indicates MSI-L or MSS.
4. No signs of intestinal obstruction; or intestinal obstruction that has been relieved after proximal colostomy.
5. No prior rectal surgery; no prior systemic anti-cancer therapy, or other investigational drug therapy.
6. Age ≥18 years, both sexes eligible.
7. Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0 or 1.
8. Expected survival of ≥2 years.
9. Adequate bone marrow and organ function. Exclusion Criteria

1. Currently participating in another interventional clinical study, except for observational (non-interventional) clinical studies or those in the survival follow-up phase of an interventional study.

2. Plans to receive other anti-tumor therapy during the treatment period of this study.

3. Receipt of any live vaccine within 4 weeks before the first dose of study drug, or plans to receive any live vaccine during the study period.

4. Presence of toxicity from prior therapy that has not recovered to Grade 0 or 1 per NCI CTCAE V6.0 before the first dose of study drug (excluding alopecia, fatigue, pigmentation, and other conditions judged by the investigator to pose no safety risk).

5. Major surgery 6. Receipt of immunosuppressive therapy within 4 weeks before the first dose of study drug, excluding topical corticosteroids administered intranasally, by inhalation, or by other local routes, or physiological doses of systemic corticosteroids , or corticosteroids used to prevent contrast agent allergy.

7. Recurrent rectal cancer; multiple primary colorectal cancers. 8. History of pelvic or abdominal radiotherapy.