Nasopharyngeal carcinoma (NPC) is notorious for the metastases, which are in close association with Epstein-Barr virus-encoded latent membrane protein 1 (LMP1). Arsenic trioxide (As 2 O 3 ) has been shown to induce apoptosis and differentiation in NPC xenografts. Then, can it repress the cancer cells' metastasis potential? To elucidate this issue, the present study was performed. LMP1-negative cell line HNE1 and LMP1-positive cell line HNE1-LMP1 were used as in vitro model. Cells (1 x 10 5 /mL) were cultured with or without 3 µM As 2 O 3 for 48 h. Then the survival cells were collected to investigate their potential of colony formation, attachment, invasion, and migration. Both confocal immunofluorescence staining and Western blot were used to detect the changes of LMP1 expression. The changes of MMP-9 were examined by RT-PCR assay and Western blot. The results were as follow: i) the colony formation inhibition rate (75.41 ± 3.9% in HNE1-LMP1 cells vs 37.89 ± 4.9% in HNE1 cells), the rate of attachment (HNE1-LMP1 vs HNE1: 56.40 ± 3.5 vs 65.87 ± 5.9%), the invasion inhibitory rate (HNE1-LMP1 vs HNE1: 56.50 ± 3.7 and 27.91 ± 2.1%), and the migration inhibitory rate (HNE1-LMP1 vs HNE1: 48.70 ± 3.9 vs 29.19 ± 6.27%) were all significantly different between the two cell lines (P < 0.01). ii) LMP1 was down-regulated in As 2 O 3 -treated HNE1-LMP1 cells. iii) The reduction of MMP-9 was found in As 2 O 3 -treated groups, more evident in HNE1-LMP1 cells. Thus, we conclude that As 2 O 3 can reduce metastasis potential of NPC cells, involving inhibition of MMP-9 expression. LMP1 were also reduced in this process and seemed to enhance anti-metastasis activity of As 2 O 3 .

by Greedy method after propensity score matching (PSM) analysis. Survival curves were calculated by Kaplan-Meier method and compared with the log-rank test. Univariate and multivariate analyses were using the Cox proportional hazards regression model. Results: 975 patients were enrolled into the study, 510 patients (52.3%) did not receive any postoperative treatment after surgery and 465 patients had either postoperative chemoradiation or radiotherapy, 331 patients had radiotherapy and 134 had postoperative chemoradiotherapy. Median follow-up was 69.2 months (95% CI 67.1-71.4 months). The 3-year, 5-year survival rates and median survival were 43.3%，32.8%， 28.9 months. DFS rates 37.7%, 31.7% and 22.5 months; and 52.3%, 40.3%, 41.8 months, respectively (PZ0.000). After PSM, 222 well-balanced patients in each group. The 3-year, 5-year survival rates and median survival were 33.0%, 26.4%, 24.4 months; and 52.3%, 40.3%, 41.8 months, respectively (PZ0.002). 33.0%, 26.4%, 24.4 months and 48.3%, 37.1%, 34.3months. N stage and adjuvant treatment are independent prognostic factors. Comparing with radiotherapy, postoperative chemoradiation did not improve DFS and OS. Conclusion: Adjuvant treatment could improve survival for patients with stage node positive or stage III thoracic squamous cell carcinoma. Further investigation is warranted.