| Background and Objective:In endemic regions, almost 100% of undifferentiated nasopharyngeal carcinoma (NPC) carries EBV. Serological detection of Epstein-Barr virus (EBV) antibodies is frequently applied in NPC mass screening. However, the large number of seropositive subjects who require close follow-up is still a big burden. The present study aimed to detect the nasopharyngeal EBV load in a high-risk population with seropositive for antibodies against EBV and proposed that an additional detection of nasopharyngeal (NP) EBV-DNA load might reduce the number of high-risk subjects for follow-up and improve early detection of NPC.Materials and Methods:Between 2006 and 2013 a population-based NPC screening program was conducted in Cangwu County, Wuzhou, Guangxi Autonomous Region in Southern China. Three towns of Cangwu County were selected to participate in the screening program. Age 30-59 years old residents were asked to participate in the screening tests. A serum sample was taken from each subject at enrollment for detection of EBV VCA/IgA antibody by immunoenzymatic assay, and each subject was offered an otorhinolaryngologic and neck lymphatic examination. Subjects with serum immunoglobulin A (IgA) antibodies against viral capsid antigen (VCA) titers≥1:5 were defined as high-risk group, and were then follbwed-up for NPC occurrence. In 2010, a follow-up serological and endoscopy examination were performed among the high-risk subjects. Besides serological test, otorhinolaryngologic and neck lymphatic examination, these subjects were asked for donating a nasopharyngeal swab for quantitative PCR assa. The distribution of NP EBV-DNA and serum VCA/IgA were described and the relationship between these two markers was analysed in the high risk population. The levels of NP EBV-DNA and serum VCA/IgA were compared in NPC and NPC-free individuals. Series of cut-off values (COV) of VCA/IgA titers and NP EBV load were defined by calculating mean plus standard deviation (SD) from NPC-free population, then sensitivity, specificity, positive predictive value, negative prediction value of different COVs were calculated for comparison of diagnostic performance. Receiver operating characteristic curves (ROC curve) were also created to evaluate the overall diagnostic values of these two markers.Results:1. A total of 22184 subjects participated in the primary screening program, 1045 individuals were defined as high-risk group and 25 NPC cases were picked up. Eight NPC cases were found from the high-risk population in the follow-up.2. EBV-DNA from NP swab was positively detected (>0 copies/swab) in 89%(802/905) of the subjects, the median copy number was 6.7×103 copies/swab, while 11%(103/905) were undetectable (0 copies/swab).94% (847/905) of the retested VCA/IgA subjects maintained positive status (^1:5), with a mean IgA antibody titer 1:10.7.3. The NP swab EBV-DNA load in female was higher than that in male with a ratio of nearly 2 fold (Z=-3.257, P= 0.001). Whereas no statistically difference between male and female for VCA/IgA titers (Z=-0.372, P=0.710). EBV-DNA load and VCA/IgA in older group were higher than that in younger group, both marks tended to increase with age, while the association was not statistically significant (Spearman’s correlation coefficient was 0.139, P< 0.001; 0.104, P=0.002, respectively).4. NP EBV-DNA copy numbers increased with increasing serum VCA/IgA antibody titers, with a weak correlation was observed (Spearman’s correlation coefficient=0.229, P< 0.001). The result remained unchanged after multivariate adjustment for age, sex, and swab β-globin copy numbers.5. Eight individuals were diagnosed with NPC by pathological examination in the 905 NPC high-risk subjects during follow-up.7 of the 8 cases were early-stage NPCs. The NP EBV load of the NPCs was significantly higher than that of NPC-free high-risk individuals (Z=-4.688, P< 0.001). A significantly higher VCA/IgA titer was also observed in NPCs (Z=-4.097, P<0.001). Both the EBV load and VCA/IgA titer of the NPC patients showed no correlation to the clinical stage (Spearman’s correlation coefficient was 0.385, P＝0.346; 0.193, P=0.648, respectively).6. The optimal cut-off value (COV) of EBV load was mean+2SD (i.e. 4.7×105 copies/swab) with sensitivity, specificity, positive predictive value, negative prediction value were 87.5%,98.9%,41.2%,99.9%, respectively. In contrast, the best COV of VCA/IgA was mean+SD (i.e.1:20), the sensitivity, specificity, positive predictive value, negative prediction value were 87.5%, 75.0%,3.1%,99.9%, respectively. The area under the ROC curve (AUC) of EBV load was larger than that of VCA/IgA, the AUC of EBV load and VCA/IgA titers were 0.980,0.895, respectively. More importantly, over 95% subjects in this study were under the EBV-DNA cut-off value could be defined as negative subjects and would be excluded from further follow-up, thus reduce the number of subjects needed to be closely followed up.Conclusions:1. Close to 90% of the high risk population was EBV-DNA positive at the nasopharynx.2. Female had a higher NP EBV-DNA load compared with male in the high risk population. The NP EBV-DNA load showed no correlation to age.3. NP EBV-DNA copy numbers increased with increasing serum VCA/IgA antibody titers.4. Both the NP EBV load and serum VCA/IgA antibody titers of the NPCs was significantly higher than that of NPC-free high-risk individuals and showed no correlation to the clinical stage.5. NP EBV load had a high diagnostic performance compared with VCA/IgA. An additional assay of EBV load in the nasopharynx among high-risk individuals might improve the possibility of detection of early-stage NPC and might reduce the number of subjects needed to be closely followed up and could serve as part of a NPC screening program in high-risk populations. |
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