Fluctuations of epstein-barr virus serological antibodies and risk for nasopharyngeal carcinoma: a prospective screening study with a 20-year follow-up

Abstract

Background: The impact of variation of Epstein-Barr virus (EBV) antibody titers before the development of nasopharyngeal carcinoma (NPC) is still unclear. We analyzed the fluctuations of antibodies against EBV before histopathological diagnosis to assess the risk of NPC and aimed to provide a reliable basis for screening in high risk populations.

Methods: This study was based on a population-based screening program in Sihui County in Guangdong Province of China. A total of 18,986 subjects were recruited in 1987 and 1992, respectively. Baseline and repeated serological tests were performed for IgA antibodies against EBV capsid antigen (VCA/IgA) and early antigen (EA/IgA). Follow-up until the end of 2007 was accomplished through linkage with population and health registers. Cox proportional hazards regression model was used to estimate the relative risk of NPC in association with EBV antibodies. Time-dependent receiver operating characteristic curve (ROC) analysis was used to further evaluate the predictive ability.

Results: A total of 125 NPCs occurred during an average of 16.9 years of follow-up. Using baseline information alone or together with repeated measurements, serological levels of VCA/IgA and EA/IgA were significantly associated with increased risks for NPC, with a striking dose-response relationship and most prominent during the first 5 years of follow-up. Considering the fluctuant types of serological titers observed during the first three tests, relative risk was highest among participants with ascending titers of EBV VCA/IgA antibodies with an adjusted hazard ratio (HR) of 21.3 (95% confidence interval [CI] 7.1 to 64.1), and lowest for those with decreasing titers (HR = 1.5, 95% CI 0.2 to 11.4), during the first 5 years of follow-up. Time-dependent ROC analysis showed that VCA/IgA had better predictive performance for NPC incidence than EA/IgA.

Conclusion: Our study documents that elevated EBV antibodies, particularly with ascending titers, are strongly associated with an increased risk for NPC.

Figure 1. Cumulative probability of developing nasopharyngeal carcinoma (NPC) during follow-up among 18,411 subjects, according to baseline levels of IgA antibodies against EBV capsid antigen (VCA/IgA) (1987–2007).

Figure 2. Variation of IgA antibodies against Epstein-Barr virus capsid (VCA/IgA) or early antigen (EA/IgA) over time in 42 subjects who developed nasopharyngeal carcinoma (NPC) during follow-up and in 1,276 subjects who were NPC-free by the end of follow-up, among the group baseline seropositive for VCA/IgA (1,318 subjects).

Note: Geometric means of serolgocial titres in each follow-up year were calculated. Specifically, the numbers of tests were 42, 37, 18, 19, 5, 16 and 11 for baseline, 1st year, 2nd year, 3rd year, 4th year, 5th year and 6th or more year of follow-up, respectively in NPC group. The numbers of tests were 1276, 1217, 615, 813, 287, 1008 and 708 for baseline, 1st year, 2nd year, 3rd year, 4th year, 5th year and 6th or more year of follow-up, respectively in NPC-free group.

Figure 3. Time-dependent ROC curve analysis for nasopharyngeal carcinoma (NPC) prediction according to baseline levels of IgA antibodies against EBV capsid antigen (VCA/IgA) and early antigen (EA/IgA) (ordinal categorical variable).

ROC, receiver operating characteristic; AUC, area under the ROC curve, NPC, nasopharyngeal carcinoma.

Figure 4. Protocol of Serological Tests for Anti-Epstein-Barr Virus Antibodies in the Nasopharyngeal Carcinoma Screening Cohort from 1987 to 2007 in Sihui, Guangdong, China.

Figure 5. Graph of displaying different fluctuation patterns in 962 subjects seropositive for baseline VCA-IgA test and with at least 2 repeated tests during the first 5 years of follow-up.

The red arrow shows that titers of VCA/IgA were higher than those in the previous test. The blue arrow shows that titers of VCA/IgA were equal to those in the previoust test. The green arrow shows that titers of VCA/IgA were lower than those in the previous test. Therefore, according to the definition, 129 (21+70+38) subjects were classified into the Ascending group, 407 (72+279+56) into the Descending group and 426 (178+26+222) into the Stable group. VCA/IgA, IgA antibodies against EBV capsid antigen; EA/IgA, IgA antibodies against EBV early antigen. Definition: Ascending group: Subjects whose repeated antibody titres were equal or higher than those in the previous test and the titres in the 3rd test were higher than the baseline. Descending group: Subjects whose repeated antibody titres were equal or lower than those in the previous test and the titres in the 3rd test were lower than the baseline. Stable group: The rest of subjects.