This is a single arm, open-label, prospective clinical trial to evaluate the combination of neoadjuvant short-course radiotherapy and toripalimab (PD-1 antibody) for locally advanced rectal cancer (LARC) patients with high risk factors. A total of 53patients will be enrolled in this trial to receive 5*5Gy short-course radiotherapy, followed by 4 cycles of CAPOX chemotherapy and PD-1 antibody. Then they will receive the TME surgery and another 2 cycles of CAPOX chemotherapy. The primary end point is the rate of pathological complete response (pCR). The long-term prognosis and adverse effects will also be evaluated and analyzed.

Inclusion Criteria:

• Age 18-75 years old, female and male;
• Pathological confirmed MSS or pMMR rectal adenocarcinoma;
• Clinical stage T3-4 (AJCC 8th) and at least with one high risk factor（CRM+ or EMVI+ or lateral lymph nodes+）;
• No previous chemotherapy, radiotherapy, immunotherapy or other anti-tumor treatment;
• Adequate organ function defined at baseline as:

ANC ≥1.5××109/L，PLt ≥100×109 /L，Hb ≥90 g/L，15×109 /L≥WBC≥4×109 /L; TBIL ≤1.5×ULN, ALT ≤1.5ULN, AST ≤1.5ULN, BUN and Cr ≤1.5×ULN or Ccr

• 60ml/min (Cockcroft-Gault formula);INR ≤1.5×ULN or PT ≤1.5×ULN (when patient didn't accept anticoagulant therapy);

  • Women of childbearing age must have taken reliable contraceptive measures or have a pregnancy test (serum or urine) within 7 days prior to enrollment and the results are negative;

Exclusion Criteria:

• Pathological confirmed rectal squamous cell carcinoma;
• History of other uncured malignancies within 5 years;
• Allergic to any component of chemotherapy or immunotherapy;
• History of any active, known, or suspected autoimmune disease, including but not limited to myasthenia gravis,Myositis, autoimmune hepatitis, systemic lupus erythematosus, rheumatoid arthritis,Inflammatory bowel disease, vascular thrombosis associated with antiphospholipid syndrome, Wegener granulation Swollen disease, Sjogren's syndrome, Guillain-Barre syndrome, multiple sclerosis, vasculitis or Glomerulonephritis.
• With congenital or acquired immunodeficiency (such as those with HIV infection), active hepatitis B or hepatitis C;