Synergistic Association of Hepatitis B Surface Antigen and Plasma Epstein-Barr Virus DNA Load on Distant Metastasis in Patients With Nasopharyngeal Carcinoma

IMPORTANCE: Hepatitis B surface antigen (HBsAg) reportedly increases the risk of distant metastasis among patients with nasopharyngeal carcinoma (NPC). However, the associated potential interaction and changes in hazard ratios (HRs) between HBsAg and different plasma Epstein-Barr (EBV) DNA levels are unknown. Moreover, the potential HBsAg-positive–associated NPC metastatic mechanism remains unclear. OBJECTIVE: To investigate the prognostic value and biological associations of HBsAg and plasma EBV DNA levels on distant metastasis in patients with NPC. DESIGN, SETTING, AND PARTICIPANTS: Retrospective cohort study performed at Sun Yat-sen University Cancer Center between January 2010 and January 2013. A total of 792 patients with nonmetastatic NPC were enrolled. The median (range) follow-up time was 62.1 (1.4-83.4) months. Of these patients, 17.8% presented with HBsAg positivity. Cytological experiments were performed to evaluate the role of HBsAg in the invasion and migration of EBV-positive NPC cells. Data analysis was performed from July 2020 to April 2021. MAIN OUTCOMES AND MEASURES: The primary end point was distant metastasis–free survival. Association rules were used to identify new rules related to distant metastasis. Interaction plots, univariate and multivariate Cox regression analyses, stratification analysis, and quantification using HRs were conducted. Additionally, cell migration and invasion assays, as well as Western blotting, were performed in the cytological validation. RESULTS: Among the 792 patients, 576 (72.7%) were male, with a median (IQR) age of 45 (38-53) years. The HBsAg-positive group exhibited a significant interaction and increased risk of distant metastasis when plasma EBV DNA cutoff levels were 1.5 × 1000 copies/mL or greater. The HR was 9.16 (95% CI, 2.46-34.14) when the plasma EBV DNA load reached 6 × 1000 copies/mL, which was higher than that in patients with stage IV disease (HR, 2.01; 95% CI, 1.13-3.56; P = .02). In cytological experiments, HBsAg promoted epithelial-mesenchymal transition by upregulating vimentin and fibronectin in EBV-positive NPC cells in vitro, thereby promoting invasion and migration of EBV-positive NPC cells. CONCLUSIONS AND RELEVANCE: In this cohort study, the observed synergistic association between HBsAg and plasma EBV DNA load represented a novel potential mechanism underlying the increased risk of distant metastasis in patients with NPC. Hence, attention should be paid to patients with NPC with HBsAg positivity, especially when the plasma EBV DNA level is 6 × 1000 copies/mL or greater. Consideration of this synergistic association will contribute to more accurate individualized management.