Node-sparing Short-Course Radiation Combined With CAPOX and Tislelizumab for MSS Rectal Cancer

Inclusion Criteria:

1. Patients who have a strong willingness to preserve the anus and are willing toreceive neoadjuvant therapy.

2. Male or Female aged 18-75.

3. Patients diagnosed with low rectal cancer within 10 cm from the lower edge of thetumor to the anal verge by pelvic MRI and anorectoscopy, the clinical stage iscT3-4bN0/+M0, and the lymph nodes are limited to the mesorectum.

4. Histologically confirmed rectal adenocarcinoma; Genetic testing suggests MSI-L orMSS, or tumor biopsy immunohistochemistry reveals pMMR, that is, MSH1, MSH2, MSH6,and PMS2 are all positive.

5. Eastern Cooperative Oncology Group (ECOG) score 0-1.

6. No previous treatment (including anti-tumor therapy, immunotherapy or pelvicradiation).

7. Laboratory tests indicating no contraindications to radiotherapy, chemotherapy andimmunotherapy.

8. Informed consent form signed.

Exclusion Criteria:

1. Patients with a previous history of malignant tumors besides rectal cancer.

2. Patients with distant metastases before enrollment.

3. Patients with positive internal or external iliac lymph nodes are assessed by MRI orCT.

4. Patients with obstruction, perforation, or bleeding that require emergency surgery.

5. Patients with severe concomitant diseases and estimated survival time ≤ 5 years.

6. Allergic to any component of the therapy.

7. Patients who received immunosuppressive or systemic hormone therapy forimmunosuppressive purposes within 1 month prior to the initiation of therapy.

8. Patients who have received any other experimental drug (including immunotherapy) orparticipated in another interventional clinical trial within 30 days beforescreening.

9. Factors leading to study termination, such as alcoholism, drug abuse, other seriousillnesses (including psychiatric disorders) requiring combination therapy, andpatients with severe laboratory abnormalities.

10. Patients with congenital or acquired immune deficiency (such as HIV infection).

11. Vulnerable groups, including mentally ill, cognitively impaired, critically illpatients, minors, pregnant or lactating women, illiterate, etc.

12. Other conditions that investigators consider not suitable for this study.