PD-1 Blockade Combined with Chemotherapy Followed by Concurrent Immunoradiotherapy for Locally Advanced SCCA Patients

Inclusion Criteria: (1) Histology confirmed as anal canal squamous carcinoma; 1. Clinical stage I-III 2. No distant metastasis; 3. Age: 18-75 years old; 4. ECOG 0-1 score 5. Adequate bone marrow, liver, kidney function 6. if HIV infected, HIV loading is below the lower limit (\<20 copy \</ ml), with the number of CD4+T cells \> 300\> ml 7. Non-pregnant or lactating women; 8. No other malignant disease within 5 years before diagnosis of anal cancer squamous carcinoma (except endocervical cancer in situ or skin basal cell carcinoma which had been cured); no other malignant disease beside anal cancer squamous carcinoma 9. No other serious disease leading to shortened survival. 10. No previous anal canal surgery or anal tumor resection (except for biopsy); 11. No chemotherapy received within the previous 5 years; 12. No previous pelvic radiation; 13. No biological treatment received in the previous 5 years; 14. No previous immunotherapy received. Exclusion Criteria: 1. Diagnosed as stage I and well differentiated squamous cell carcinoma 2. Distant metastasis 3. Received radiation therapy in abdominal or pelvic regions 4. Pregnant, lactating woman patient or fertile but lacks adequate contraceptives 5. Infectious disease: Active phase chronic hepatitis B or hepatitis C (high copies of virus DNA); Other serious active clinical infection 6. Patients with active tuberculosis (TB) are receiving anti-tuberculosis treatment or have received anti-tuberculosis treatment within 1 year before screening; 7. Chronic inflammatory colorectal disease, unrelieved ileus 8. Dyscrasia or organ decompensation 9. Allergic to research-related drugs 10. Severe hypertension with poor drug control; 11. Epilepsy require medical treatment (such as steroid or antiepileptic therapy); 12. Drug abuse and medical, psychological or social factors that may interfere with patients' participation in the study or affect the evaluation of the study; 13. Patients have any active autoimmune diseases or a history of autoimmune diseases (including but not limited to: interstitial pneumonia, uveitis, enteritis, hepatitis, hypophysitis, nephritis, hyperthyroidism and decreased thyroid function; patients with vitiligo or with complete remission of asthma in childhood and without any intervention in adulthood may be included; patients with asthma requiring bronchodilators intervention are not included. 14. Received any anti-infection vaccine (e.g. influenza vaccine, chickenpox vaccine, etc.) within 4 weeks before enrollment; 15. Complications require long-term treatment with immunosuppressive drugs, or requiring systemic or local use of immunosuppressive corticosteroids(\>10mg/day prednisone or other therapeutic hormones); 16. Any unstable condition or which endangers the patients' safety and compliance; 17. Refuses to sign informed consent