Inclusion Criteria:

          1. Biopsy proven nasopharyngeal carcinoma, with detectable pretreatment plasma EBV DNA

          2. Have detectable plasma EBV DNA at the end of (+/- 1 week) curative radiotherapy or
             chemoradiotherapy (radiation dose > 66Gy), determined by the central lab

          3. No clinical evidence of persistent loco-regional disease

          4. No evidence of distant metastasis, based upon skeletal scintigraphy, chest X-ray
             examination, and liver ultrasound or other appropriate workup (e.g., CT, MRI or
             positron emission tomography (PET)/CT]) within 21 days prior to registration

          5. Eastern Cooperative Oncology Group (ECOG) performance status 0-1

          6. Anticipated survival >= 3 months

          7. Absolute neutrophil count (ANC) >= 1,500 cells/mm^3

          8. Platelets > 80,000 cells/mm^3

          9. Hemoglobin >= 8.0 g/dl (no transfusion within the last 14 days)

         10. Total bilirubin =< 1.5 x institutional upper limit of normal (ULN)

         11. Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) =< 2.5 x
             institutional ULN

         12. Creatinine clearance (CC) >= 50 ml/min estimated by Cockcroft-Gault formula

        Exclusion Criteria:

          1. Patients with stage III-IV disease (American Joint Committee On Cancer/Union for
             International Cancer Control 7th) and no contraindication to chemotherapy that didn't
             receive platinum based concurrent chemotherapy during radiation

          2. Patients with tumor possibly invaded main vessels (e.g. encasement of the internal
             jugular artery/vein) at diagnosis; or tumor that, in the judgment of the investigator,
             likely to invade main vessels and cause life-threatening hemorrhage events during
             study

          3. History of serious hemorrhage events or grade 3 or higher hemorrhage within 4 weeks
             prior to registration

          4. Hypertension that couldn't be well controlled with single medication; unstable angina;
             angina diagnosed within the last 3 months; myocardial infarction within the last 6
             months; cardiac arrhythmia that need long-term medication; grade 2 or higher cardiac
             dysfunction (NYHA)

          5. Proteinuria

          6. Coagulation dysfunction or predisposition to hemorrhage; on treatment of
             anticoagulation medication or vitamin K antagonist; low dose warfarin (1mg po qd) or
             aspirin (less than 100mg daily) were permitted as long as the international normalized
             ratio (INR) = < 1.5

          7. Thrombosis within the last 1 year, except cured vein thrombosis related to vein
             indwelling catheter

          8. Unhealed bone fracture or chronic unhealed wound

          9. Illness that would interfere with oral medication, including dysphagia, chronic
             diarrhea, or ileus

         10. Pregnant or lactating women

         11. Women of childbearing potential and men who are sexually active and not willing/able
             to use medically acceptable forms of contraception during and within 6 months after
             study

         12. Current drug abuse or mentally disabled

         13. History of congenital or acquired immune deficiency disease or organ transplantation

         14. Major medical illness, which in the investigator's opinion would endanger the patients
             or interfere with the completion of therapy and follow up