Preoperative Short-course Radiation Followed by Envafolimab Plus CAPEOX for MSS Locally Advanced Rectal Adenocarcinoma (PRECAM)

Inclusion Criteria:

1. Patients who are willing to receive neoadjuvant therapy.

2. ≧18 years old.

3. Diagnosed by digital rectal examination, colonoscopy, and high-resolution MRI of thepelvis, the tumor is less than or equal to 12 cm from the anus.

4. Histologically diagnosed as rectal adenocarcinoma.

5. The clinical staging by pelvic contrast-enhanced CT and pelvic high-resolution MRIwere cT2-4a N+, cT3/T4a N0.

6. MMR protein detection or MSI gene detection of rectal cancer specimens confirmedpMMR or MSS before treatment .

7. The patient has good compliance and can come to the hospital for re-examination asrequired.

8. ECOG Scale of Performance Status score 0-1 point.

9. Have not received anti-tumor and immunotherapy before enrollment.

10. Laboratory inspections must meet the following standards:

11. White blood cell count>3.5×109/L, absolute value of neutrophils>1.8×109/L,platelet count ≥75×109/L, hemoglobin ≥100g/L;

12. INR≤1.5, and APTT≤1.5 times the upper limit of normal or partial prothrombintime (PT) ≤1.5 times the upper limit of normal;

13. Total bilirubin ≤ 1.25 times the upper limit of normal; ALT and AST < 5 timesthe upper limit of normal;

14. 24h creatinine clearance >50mL/min or serum creatinine <1.5 times the upperlimit of normal.

15. Voluntarily participate in this study and sign the informed consent.

Exclusion Criteria:

1. History of other malignant diseases in the past 5 years.

2. Patients with metastases from other sites (stage IV patients).

3. Patients with clinical staging of T1-2N0 or T4b, or positive lateral lymph nodes bypelvic contrast-enhanced CT and pelvic high-resolution MRI.

4. Patients with intestinal obstruction, intestinal perforation, intestinal bleeding,etc. requiring emergency surgery.

5. Known allergic to oxaliplatin, capecitabine, PD-L1 monoclonal antibody and otherdrugs.

6. Pathologically suggested signet ring cell carcinoma and mucinous adenocarcinoma.

7. dMMR or MSI-H patients.

8. The patient is accompanied by any unstable systemic disease, including but notlimited to: severe infection, uncontrolled diabetes, hypertension uncontrolled bymedication, unstable angina, cerebrovascular accident or transient cerebralischemia, myocardial Infarction, congestive heart failure, severe cardiac arrhythmiarequiring medication, hepatic, renal or metabolic disease; disease affecting thepatient's life.

9. The disease (such as mental illness, etc.) or condition (such as alcoholism or drugabuse, etc.) associated with the patient will increase the risk of the patientreceiving the trial drug treatment or affect the patient's compliance with the trialrequirements, or may confuse the research results.

10. Active autoimmune disease that may worsen while receiving immunostimulants.

11. Known history of positive HIV test or known acquired immunodeficiency syndrome.

12. Patients who are using immunosuppressive agents, except for the followingconditions:

13. Intranasal, inhaled, topical steroids, or topical steroid injections (eg,intra-articular injections);

14. Physiological doses of systemic corticosteroids ≤10 mg/day prednisone orequivalent;

15. Steroids used to prevent allergic reactions (eg, before CT scan).

16. Received any other experimental drug treatment or participated in anotherinterventional clinical trial within 30 days before screening

17. Women who are pregnant or breastfeeding or who plan to become pregnant orbreastfeeding during the study period; men or women who are unwilling to takeeffective contraceptive measures.

18. Vulnerable groups, including mentally ill, cognitively impaired, critically illpatients, minors, etc.

19. Other conditions that the investigator judges that the patient is not suitable toparticipate in the clinical study, etc.