Background & objective: Epstein-Barr virus (EBV) closely relates to nasopharyngeal carcinoma (NPC). Whether EBV is a causative viral agent or a by-stander in the carcinogenesis of NPC needs further study. The latent status of EBV during carcinogenesis of NPC remains unknown nowadays. This study was to explore the infectious status of EBV in NPC, and analyze the correlation of EBV to carcinogenesis of NPC.
Methods: Carcinoma tissues,adjacent tissues, and contralateral normal nasopharyngeal tissues from 47 patients with poorly-differentiated nasopharyngeal squamous cell carcinoma were prepared simultaneously. Nasopharyngeal tissues from 10 healthy subjects were used as control. EBV DNA copies levels in the specimens were tested using real-time quantitative polymerase chain reaction (PCR); localization of EBV was detected by in situ hybridization [digoxigenin-labeled EBV-encoded RNA 1 (EBER-1) probe].
Results: Infectious rate of EBV was 80.0% in nasopharyngeal tissues of healthy subjects (mean EBV DNA copies of 6.7x10(2)/microg DNA), 100% in carcinoma tissues and adjacent tissues of NPC patients, and 72.3% in contralateral normal nasopharyngeal tissues of NPC patients (mean EBV DNA copies of 6.9x10(5)/microg DNA, 1.5x10(5)/microg DNA, and 9.8x10(3)/microg DNA, respectively). There was no significant difference in infectious rate and level of EBV between controlateral normal nasopharyngeal tissues of NPC patients and nasopharyngeal tissues of healthy subjects (P>0.05); infectious level of EBV was significantly higher in carcinoma tissues than in adjacent tissues (P<0.05), and significantly higher in adjacent tissues than in contralateral normal nasopharyngeal tissues of NPC patients (P<0.01). Using in situ hybridization, EBER-1 expression signal was not detected in contralateral normal nasopharyngeal epithelia of NPC patients, weak in atypical hyperplastic cells in adjacent tissues, and strong in carcinoma cells.
Conclusions: EBV latent infection is a common phenomenon in nasopharyngeal tissues of both NPC patients and healthy persons. The enhancement of EBV infection plays an important role during carcinogenesis of NPC.