Table 1.

Inclusion and exclusion criteria

Inclusion criteria

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

2. Male or female aged 18–75 years.

3. Patients diagnosed with low rectal cancer within 10 cm from the lower edge of the tumour to the anal verge by pelvic MRI and anorectoscopy, the clinical stage is cT2N + M0/cT3-4bN0/+M0, the lymph nodes are limited to the mesorectum.

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

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

6. No previous treatment (including antitumour therapy、immunotherapy or pelvic radiation).

7. Adequate haematologic, hepatic, renal, thyroid and cardiac function: white blood cells ≥ 3500/mm3, neutrophils ≥ 1800/mm3, platelets ≥ 100,000/mm3, haemoglobin ≥ 100 g/L; activated partial thromboplastin time, prothrombin time and international normalized ratio ≤ 1.5 × ULN; aspartate aminotransferase and alanine aminotransferase ≤ 3.0 × upper limit of normal (ULN), bilirubin ≤ 1.25 × ULN, serum albumin ≥ 28 g/L, creatinine clearance ≥ 50 mL/mi, creatinine ≤ 1.5 × ULN.

8. Informed consent form signed.

Exclusion criteria

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

2. Patients with distant metastases before enrolment.

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

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 with poorly differentiated adenocarcinoma, signet ring cell carcinoma, or mucinous adenocarcinoma.

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

9. Patients who have received any other experimental drug (including immunotherapy) or participated in another interventional clinical trial within 30 days before screening.

10. Factors leading to study termination, such as alcoholism, drug abuse, other serious illnesses (including psychiatric disorders) requiring combination therapy, and patients with severe laboratory abnormalities.

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

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

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