The purpose of this study is to examine the efficacy of maintenance chemotherapy for the treatment of metastatic nasopharyngeal carcinoma. Participants will be randomized to 3 arms. Arm 1, control group, participants will receive only 4-8 cycles of conventional chemotherapy; arm 2, participants will receive 6 cycles of maintenance chemotherapy after conventional chemotherapy; arm 3, experiment arm, after conventional chemotherapy, participants will receive maintenance chemotherapy until disease progression or intolerable toxicities.