Trial Evaluating Maintenance Chemotherapy for Metastatic Nasopharyngeal Carcinoma

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.