PD-1 Antibody Versus Best Supportive Care After Chemoradiation in Locoregionally Advanced Nasopharyngeal Carcinoma

Inclusion Criteria: * Patients with histologically confirmed nasopharyngeal carcinoma. * Tumor staged as III-IVA (AJCC 8th, except T3N0-1 or T4N0). * Completed protocol-specified curative chemoradiotherapy, including gemcitabine and cisplatin induction chemotherapy, intensity-modulated radiotherapy, and concurrent cisplatin chemotherapy. * Completion of the last radiation dose within 1 to 42 days before randomization * Eastern Cooperative Oncology Group performance status ≤1. * Adequate marrow function: neutrocyte count≥1.5×10e9/L, hemoglobin ≥90g/L and platelet count ≥100×10e9/L. * Alanine Aminotransferase (ALT)/Aspartate Aminotransferase (AST) ≤2.5×upper limit of normal (ULN), and bilirubin ≤ 1.5×ULN. * Adequate renal function: creatinine clearance rate ≥ 60 ml/min (Cockcroft-Gault formula). * Patients must be informed of the investigational nature of this study and give written informed consent. * Women of childbearing potential (WOCBP) who are sexually active must be willing to adhere to effective contraception during treatment and for 1 year after the last dose of study drug. Men who are sexually active with WOCBP must be willing to adhere to effective contraception during treatment and for 1 year after the last dose of the study drug. Exclusion Criteria: * Age \> 65 or \< 18. * Hepatitis B surface antigen (HBsAg) positive and hepatitis B virus DNA \>1×10e3 copies/ml or 200IU/ml * Hepatitis C virus (HCV) antibody positive * Has active autoimmune disease, except type I diabetes, hypothyroidism treated with replacement therapy, and skin disease that doesn't require systemic treatment (e.g., vitiligo, psoriasis, or alopecia). * Has any condition that required systemic corticosteroid (equivalent to prednisone \>10mg/d) or other immunosuppressive therapy within 28 days before informed consent. Patients received systemic corticosteroid equivalent to prednisone ≤10mg/d, inhale or topical corticosteroid will be allowed. * Has a known history of active TB (bacillus tuberculosis) within 1 year; patients with adequately treated active TB over 1 year ago will be allowed. * Has a known history of interstitial lung disease. * Has received a live vaccine within 30 days before informed consent or will receive a live vaccine in the near future. * Is pregnant or breastfeeding. * Prior malignancy within 5 years, except in situ cancer, adequately treated non-melanoma skin cancer, and papillary thyroid carcinoma. * Has known allergy to large molecule protein products or any compound of camrelizumab. * Has a known history of human immunodeficiency virus (HIV) infection. * Any other condition, including symptomatic heart failure, unstable angina, myocardial infarction, active infection requiring systemic therapy, mental illness or domestic/social factors, deemed by the investigator to be likely to interfere with a patient's ability to sign informed consent, cooperate and participate in the study, or interferes with the interpretation of the results.