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Original Article

Circulating Plasma Epstein-Barr Virus DNA Load During the Follow-up Periods Predicts Recurrence and Metastasis in Nasopharyngeal Carcinoma

He, Sha-sha MD; Wang, Yan MD; Yang, Yun-ying BD; Niu, Shao-qing PhD; Zhu, Mei-yan MD; Lu, Li-xia PhD; Chen, Yong MD

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doi: 10.1097/PPO.0000000000000581
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The incidence of nasopharyngeal carcinoma (NPC) has remained consistently high in endemic regions such as Southern China and Southeast Asia, with a peak incidence of 50 cases per 100,000 individuals.1,2

According to the National Comprehensive Cancer Network guidelines,3 radiotherapy is the primary treatment for NPC, combined with different chemotherapeutic strategies according to the disease staging. Concurrent chemoradiotherapy is the standard option for locoregionally advanced NPC. With the improved local control and survival resulting from more precise imaging and radiotherapy, distant metastasis has become the main cause of failure of this mode of treatment.4

Positive rescue treatment is necessary for locoregional recurrence and distant metastasis of NPC and can achieve some level of curative success. In Sun Yat-Sen University Cancer Center (SYSUCC), treatment of 132 patients with recurrent NPC with intensity-modulated radiotherapy (IMRT) resulted in a 3-year local progression-free survival (PFS) and overall survival (OS) rates of 85.3% and 41.6%, respectively.5 Cervical residual lesions can be treated effectively by surgical resection. Improvements in chemotherapy and the application of targeted therapy for distant metastasis of NPC have greatly improved the efficacy of rescue treatment and further improved patients' survival.6

Early diagnosis of recurrence and metastasis is the key to improve the efficacy of rescue treatment.7 For all patients, regular review is conducted every 4 to 6 months after 3 to 5 years of treatment, and imaging is the main monitoring method. The scattered nature of recurrent tumor cells after radiotherapy renders biopsy unreliable for diagnosis, leading to a delay in rescue treatment of more than 10 weeks.8 Fludeoxyglucose–positron emission tomography provides higher sensitivity and specificity for the diagnosis of recurrence and metastasis than does computed tomography (CT) or magnetic resonance imaging, although the examination is expensive.9,10 Therefore, a sensitive, cost-effective, and practical diagnostic index is required.

We have previously reported the potential benefits of adjuvant treatment for patients with detectable Epstein-Barr virus DNA (EBV DNA) load at the end of treatment,11 in addition to the prognostic value of EBV DNA concentrations during treatment.12 Tumor response and patient survival can also be predicted based on the clearance rates of plasma EBV DNA during the first month of chemotherapy. Therefore, early changes in the chemotherapy regimen may be considered for patients with a slow plasma EBV DNA clearance rate.13 Furthermore, EBV DNA may be useful for identifying high-risk patients and guiding individual therapy in NPC. Moreover, because patients with recurrent and metastatic NPC have significantly higher EBV DNA than do patients in clinical remission (P < 0.01), EBV DNA is implicated as a sensitive tumor marker for monitoring tumor recurrence and metastasis after radiotherapy in NPC.14–16

The mechanism underlying the role of EBV DNA in NPC remains unclear, and no risk classification has been effectively demonstrated; however, previous studies have focused on the dynamic changes in viral load during the follow-up. Thus, in this study, we hypothesized that the dynamic changes in plasma EBV DNA after treatment can be used to predict recurrence or metastasis of NPC. To better assess the correlation of survival with EBV DNA during the follow-up, we performed 12- and 24-month landmark analyses.



From January 2010 to September 2013, 900 consecutive patients who had confirmed diagnosis of nonmetastatic NPC and received radical radiotherapy in SYSUCC were enrolled for initial screening. The selection criteria were as follows: (1) good performance status (Karnofsky Performance Status score ≥80); (2) normal renal, cardiac, and liver function; (3) complete EBV DNA record during treatment and 3 years after treatment; and (4) complete follow-up data.


The therapeutic protocol was based strictly on the National Comprehensive Cancer Network guidelines. All patients received the following treatment: stage I, IMRT alone; stage II, IMRT with concurrent chemotherapy; and stages III and IVA–B, concurrent chemoradiotherapy with or without neoadjuvant or adjuvant chemotherapy. All patients underwent targeted radiotherapy using a thermoplastic mask based on CT simulation. Radiation Therapy Oncology Group guidelines were applied for target delineation. Planning target volume (PTV) was defined as the primary tumor (PTVp) and positive lymph node (PTVn), high-risk PTV (PTV-HR) was defined as the PTVp with an appropriate margin, and low-risk PTV (PTV-LR) was defined as PTV-HR with an appropriate margin plus the elective lymph node region. The treatment consisted of definitive radiotherapy with a total dose of 68 to 72 Gy to PTVp, 60 to 68 Gy to PTVn, 60 to 62 Gy to PTV-HR, and 50 to 54 Gy to PTV-LR. Neoadjuvant or adjuvant chemotherapy consisted of cisplatin with 5-fluorouracil or cisplatin with taxanes, or all 3 together, administered triweekly for 2 or 3 cycles. Concurrent chemotherapy consisted of cisplatin/nedaplatin administered triweekly or weekly until the end of radiotherapy.

Quantification of Plasma EBV DNA

Samples of peripheral venous blood (5 mL) were obtained from all patients. For isolation of plasma and peripheral blood cells, the blood samples were placed in EDTA-containing tubes and centrifuged at 1600g for 15 minutes. Plasma DNA was extracted using a QIAamp Blood Kit (Qiagen, Hilden, Germany). Epstein-Barr virus DNA concentrations were detected using the BamHI-W region of the EBV genome and a real-time polymerase chain reaction assay according to a previously described method.17 The sequences of the forward and reverse primers used in the assay were as follows: 5′-GCCAG AGGTA AGTGG ACTTT-3′ and 5′-TACCA CCTCC TCTTC TTGCT-3′. The dual fluorescently–labeled oligomer of 5′-(FAM) CACAC CCAGG CACAC ACTAC ACAT (TAMRA)-3′ served as the probe.


The endpoints for this study were OS, measured from the date of first NPC diagnosis to either the date of death or loss to follow-up, distant metastasis-free survival (DMFS, to distant relapse or patient censorship or death at last follow-up), locoregional-free survival (LRFS, to tumor relapse or patient censorship or death at last follow-up), and PFS (to locoregional failure, distant failure, or death from any cause, whichever occurred first). After treatment, patients were scheduled for regular follow-up visits every 3 months during the first 2 years and then every 6 months until the fifth year and yearly thereafter. Evaluations during each outpatient visit included physical examination, hematology and biochemistry profiles, magnetic resonance imaging scan, chest radiography, abdominal sonography, and a whole-body bone scan. The surveillance workup included EBV DNA load.

Statistical Analysis

Cutoff values for pretreatment plasma EBV DNA load was established using receiver operating characteristic analysis. A χ2 test was used to determine the correlation between plasma EBV DNA and treatment outcomes. A univariate logistic regression model was used to examine the association between clinical factors, EBV status, and survival outcomes. Factors with a P ≤ 0.05 in the univariate analysis were entered into the multivariate Cox regression model. Survival outcomes were estimated using the Kaplan-Meier method and compared with the log-rank test. All tests were 2-sided, and a P < 0.05 was considered statistically significant. Statistical analysis was performed using IBM SPSS software version 22.0 (IBM Corp., Armonk, NY).

The inherent statistical weakness is guarantee-time bias. As recommended by statisticians, in this study, we investigated EBV NDA as a predictor of survival by performing time-dependent response analyses using landmark and risk-of-death methods, thereby minimizing guarantee-time bias.


The study was approved by the ethics committee of SYSUCC, and the informed consent for collection and publication of medical information was obtained from all study patients at their first visit to our hospital.


Dynamic Change Patterns of EBV DNA

A total of 900 NPC patients treated at SYSUCC between January 2010 and September 2013 were retrospectively enrolled. Median age was 44 years (range, 11–77 years) and 723 of 900 patients (80.3%) were male. All patients had nonkeratinizing undifferentiated squamous cell carcinoma. According to the clinical examination during the follow-up (median, 55.78 months), there were 21 cases of nasopharyngeal locoregional recurrence, and 97 cases developed metastasis (25 cases of bone metastasis, 31 lung, 26 liver, 2 lymph node, 2 bone and lung, 2 liver and lung metastasis, 2 bone and liver, and 7 multiple sites). The baseline clinical features of the patients are shown in Table 1.

TABLE 1 - Summary of the Clinical Features of the 900 Patients With NPC Included in This Study
Characteristics Total
n (%)
900 (100)
Age, y
 <44 461 (51.2)
 ≥44 439 (48.8)
 Male 723 (80.3)
 Female 177 (19.7)
 Yes 207 (23.0)
 No 693 (77.0)
Overall stage (eighth edition)
 I 85 (9.4)
 II 231 (25.7)
 III 428 (47.6)
 IVAB 156 (17.3)
T category
 T1 210 (23.3)
 T2 142 (15.8)
 T3 427 (47.4)
 T4 121 (13.4)
N category
 N0 170 (18.9)
 N1 584 (64.9)
 N2 103 (11.4)
 N3 43 (4.8)
 IMRT 222 (24.7)
 CT + IMRT 678 (75.3)
Pre-EBV DNA (copies/mL)
 <4000 473 (52.6)
 ≥4000 427 (47.4)
Post-EBV DNA (copies/mL)
 <2500 774 (86.0)
 ≥2500 126 (14.0)
CT indicates chemotherapy; IMRT, intensity-modulated radiation therapy; N, node; NPC, nasopharyngeal carcinoma; T, tumor.

There were no patients who received adjuvant chemotherapy; at the end of radiotherapy, 25.4% of patients (229/900) (median concentration, 0 copies/mL; range, 0–26,400,000 copies/mL) were EBV DNA–positive. Pretreatment, 72.0% of patients (648/900) (median concentration, 3205 copies/mL; range, 0–49,100,000 copies/mL) were EBV DNA–positive. The posttreatment EBV DNA load was significantly lower than the pretreatment concentrations (P < 0.01).

Patients were then divided into 3 groups according to the follow-up results. Sustained remission consisted of 778 patients without recurrence or metastasis at the end of the follow-up, locoregional recurrence consisted of 21 patients with recurrence at any time point, and metastasis consisted of 97 patients with metastasis at any time point.

After radiotherapy, 39.18% of the metastatic NPC patients (38/97) (median, 0 copies/mL; range, 0–26,400,000 copies/mL) were EBV DNA–positive, and 33.33% of the recurrent NPC patients (7/21) (median, 0 copies/mL; range, 0–226,000 copies/mL) were EBV DNA–positive. In the sustained remission group (median, 0 copies/mL; range 0–843,000 copies/mL), 23.15% of patients (181/782) were EBV DNA–positive. At the end of radiotherapy, the EBV DNA load of some patients in sustained remission was still EBV DNA–positive, although the number was significantly lower than that in the other 2 groups (P = 0.01), with no significant difference between the recurrence and metastasis groups (P = 0.562).

We then evaluated the dynamic changes in EBV DNA load at each time point. At the end of therapy, the EBV DNA load decreased rapidly in the sustained remission and metastasis groups (median, 0 copies/mL). Subsequently, there was no marked change of the EBV DNA load in sustained remission group (<4000 copies/mL), although the EBV DNA load in the metastasis group increased significantly (P = 0.025), reaching a peak at 3 months followed by a decrease to 1 year, and no marked change to 3 years (<5000 copies/mL). The viral load in the recurrence group had increased rapidly 3 months after treatment and was lower than that in the metastasis group 1 year after treatment. This was followed by a gradual increase after 1 year, with a higher peak viral load in the recurrence group than that in the metastasis group, reaching 26,000 copies/mL at 12 months, 168,000 copies/mL at 24 months, and 375,000 copies/mL at 36 months, until the highest level at the time of relapse was 24,100,000 copies/mL (Fig. 1).

Change patterns of EBV DNA in the recurrence and metastasis groups during the follow-up.

Impact of EBV DNA Levels on Survival

According to the receiver operating characteristic curve analysis, the pretreatment and posttreatment cutoff values for EBV DNA were 4000 copies/mL and 2500 copies/mL, respectively. The 5-year OS, DMFS, and PFS rates for the high and low pretreatment EBV DNA levels were 83.6% and 90.0%, 84.1% and 92.9%, and 87.6% and 94.1%, respectively. These data suggest that elevated EBV DNA before treatment was associated with a poorer OS (hazard ratio [HR], 1.647, 95% confidence interval [CI], 1.126–2.408; P = 0.009; Fig. 2A). Similarly, elevated EBV DNA before treatment also indicated significantly decreased DMFS compared with lower EBV (HR, 2.377; 95% CI, 1.558–3.626; P < 0.001; Fig. 2B) and PFS (HR, 2.035; 95% CI, 1.279–3.237; P = 0.003; Fig. 2D), but not LRFS (P = 0.754; Fig. 2C).

Plasma EBV DNA before treatment higher than 4000 copies/mL is associated with poorer survival outcomes. Kaplan-Meier OS (A), DMFS (B), LRFS (C), and PFS (D).

A total of 473 patients had pretreatment EBV DNA loads below the cutoff value of 4000 copies/mL. Among them, 21 patients had posttreatment EBV DNA loads greater than 2500 copies/mL, there were 18 cases with residual tumor, 32 developed metastasis, and 45 died.

A total of 427 patients had pretreatment EBV DNA loads greater than 4000 copies/mL. Among them, 369 patients had posttreatment EBV DNA loads of less than 2500 copies/mL, 46 patients developed metastasis, eight had recurrence, and 41 died. Among the 58 of 427 patients with posttreatment EBV DNA greater than 2500 copies/mL, 19 patients developed metastasis, 4 locoregional recurrence, and 22 died, all with a higher proportion than the lower EBV ones. Thus, these data indicate that posttreatment EBV DNA load had a much more marked influence on the prognosis of patients with NPC than pretreatment EBV DNA load.

The patients were then divided into 2 groups according to the posttreatment EBV DNA cutoff values. The prognosis in the high posttreatment EBV DNA group was poorer than that of the lower EBV DNA group. Patients with posttreatment EBV DNA of less than 2500 copies/mL achieved better OS (P < 0.001), DMFS (P = 0.040), LRFS (P = 0.004), and PFS (P = 0.001) than did patients with higher posttreatment EBV DNA.

Other risk factors, including smoking, advanced tumor stage, and elevated C-reactive protein before treatment and therapy, were correlated with poor OS, DMFS, and PFS. Multivariate analyses were also performed, incorporating patient factors (age, sex, smoking), tumor factors (TNM stage), treatment methods (radiotherapy and chemotherapy), and posttreatment EBV DNA load as covariates. As shown in Table 2, posttreatment EBV DNA load was confirmed as an independent prognostic factor for OS (HR, 2.019; 95% CI, 1.305–3.122; P = 0.002), DMFS (HR, 1.565; 95% CI, 1.051–2.515; P = 0.044), LRFS (HR, 5.363; 95% CI, 2.201–7.312; P = 0.008), and PFS (HR, 1.940; 95% CI, 1.153–3.264; P = 0.013). According to these data, posttreatment EBV load had a great impact on survival and was identified as an independent prognostic factor for OS, DMFS, LRFS, and PFS.

TABLE 2 - Cox Proportional Hazards Regression Model of OS, DMFS, LRFS, and PFS
Variable Univariate Analysis Multivariate Analysis
HR (95% CI) P HR (95% CI) P
C-reactive protein (mg/L)
 ≥1.655 vs. <1.655 1.796 (1.217–2.648) 0.003
Platelet (×109/L)
 ≥268 vs. <268 1.569 (1.064–2.315) 0.023
T category
 T3–4 vs. T1–2 1.429 (1.165–1.753) 0.001
OS N category
 N2–3 vs. N0–1 2.343 (1.873–2.932) <0.001 1.573 (1.138–2.175) 0.006
Overall stage (eighth edition)
 III + IV vs. I + II 4.139 (2.362–7.253) <0.001 2.953 (1.267–6.886) 0.012
 IMRT + CT vs. IMRT 2.132 (1.662–2.736) 0.002
Post-EBV (copies/mL)
 ≥2500 vs. <2500 2.333 (1.519–3.584) <0.001 2.019 (1.305–3.122) 0.002
 Yes vs. no 1.523 (1.173–2.340) 0.045
T category
 T3–4 vs. T1–2 1.365 (1.103–1.690) 0.004 1.856 (1.051–3.279) 0.033
N category
DMFS  N2–3 vs. N0–1 7.766 (5.213–11.570) <0.001 4.411 (2.754–7.065) <0.001
Overall stage (eighth edition)
 III + IV vs. I + II 5.918 (2.981–11.747) <0.001 5.792 (2.303–14.565) <0.001
Post-EBV (copies/mL)
 ≥2500 vs. <2500 1.619 (1.010–2.595) 0.040 1.565 (1.051–2.515) 0.044
N category
 N2–3 vs. N0–1 2.630 (2.025–3.417) <0.001 2.439 (1.696–3.506) 0.018
Overall stage (eighth edition)
LRFS  III + IV vs. I + II 1.844 (1.377–2.471) <0.001 5.792 (2.303–14.565) 0.014
Post-EBV (copies/mL)
 ≥2500 vs. <2500 1.883 (1.404–2.525) <0.001 5.363 (2.201–7.312) 0.008
T category
 T3–4 vs. T1–2 1.343 (1.057–1.707) 0.016
N category
 N2–3 vs. N0–1 5.793 (3.691–9.092) <0.001 3.894 (2.346–6.464) <0.001
PFS Overall stage (eighth edition)
 III + IV vs. I + II 3.662 (1.934–6.935) <0.001 2.849 (1.161–6.994) 0.022
Post-EBV (copies/mL)
 ≥2500 vs. <2500 2.375 (1.427–3.954) 0.001 1.940 (1.153–3.264) 0.013

EBV DNA Kinetics and Survival

The 5-year OS rate for patients with sustained remission was 93.8%, which was significantly improved compared with that of the recurrence (47.6%) and metastasis (26.9%) groups (Fig. 3), with a significant difference observed between the 3 groups (recurrence vs. sustained remission: HR, 12.227; 95% CI, 6.568–22.760; P < 0.001; metastasis vs. sustained remission: HR, 15.842; 95% CI, 10.494–23.916; P < 0.001).

Plasma EBV DNA in the metastasis group and recurrence are associated with poorer OS.

According to baseline EBV DNA load and EBV kinetics, patients were further divided into 3 groups as follows: (1) continuously normal group: patients whose baseline EBV DNA normal and never elevated, 679 cases; (2) ever-elevated group: patients whose EBV DNA ever-elevated regardless time points, 97 cases; and (3) continuously elevated group: patients whose baseline EBV DNA was elevated and never normalized, 124 cases. The 5-year OS rates in the 3 groups were 93.2%, 76.2%, and 59.9%, respectively (Fig. 4A); DMFS rates were 94.4%, 84.3%, and 59.9%, respectively (Fig. 4B); LRFS rates were 98.1%, 91.5%, and 95.8%, respectively (Fig. 4C); and PFS rates were 94.8%, 83.9%, and 73.7%, respectively (Fig. 4D). There were significant differences among the 3 groups in OS (HR, 2.542; 95% CI, 2.077–3.111; P < 0.001), DMFS (HR, 2.970; 95% CI, 2.392–3.687; P < 0.001), LRFS (HR, 1.699; 95% CI, 1.072–2.692; P = 0.013), and PFS (HR, 2.535; 95% CI, 1.987–3.233; P < 0.001).

Survival outcome differences in the EBV DNA continuously normal, ever-elevated, and continuously elevated groups. Kaplan-Meier OS (A), DMFS (B), LRFS (C), and PFS (D).

Landmark Analyses

Of 900 patients in the whole group, a total of 887 patients were alive and had follow-up for at least 12 months, and therefore, they were included in the 12-month landmark analysis for survival (Fig. 5A). The 5-year OS of the 746 patients whose EBV DNA load sustained remission was 91.3%, and the elevated group was 74.4% (HR, 3.182; 95% CI, 2.114–4.788; P < 0.001).

Survival outcome differences in the EBV DNA sustained remission and elevated groups during follow-up. Twelve-month landmark (A), 24-month landmark (B).

Besides, a total of 854 patients were alive or had follow-up for at least 24 months and therefore were included in the 24-month landmark analysis for survival (Fig. 5B). The 5-year OS of the 732 patients whose EBV DNA load sustained remission was 95.0%, and the elevated group was 62.9% (HR, 9.619; 95% CI, 6.027–15.353; P < 0.001).


Many nonspecific markers have been demonstrated to play important roles in predicting tumor progression and prognosis. Epstein-Barr virus DNA load is the most representative marker in NPC18 and is widely used in screening, monitoring, and prediction of relapse in nonmetastatic NPC.19 Circulating EBV DNA concentrations correlate positively with disease stage, as well as exhibit prognostic importance in NPC.12 Based on the great variety of published studies,13,20,21 EBV DNA concentrations during treatment and plasma EBV DNA clearance rates have been identified as emerging biomarkers of survival.21,22 Furthermore, some studies have stratified the role of EBV DNA in predicting metastasis and recurrence of NPC.19 A prospective study demonstrated that EBV DNA load was a predictor of distant metastasis.23 In patients with recurrent NPC requiring salvage nasopharyngectomy, preoperative plasma EBV DNA identifies patients at high risk of subsequent distant failure after surgery. Serial measurements of plasma EBV DNA after surgery, especially for those with high preoperative levels, are crucial to allow early detection of local distant failure.24

In contrast, there were few reports describing the role of posttreatment EBV DNA in NPC, especially in-depth analysis of the dynamic changes and common variation tendencies. Li et al.25 revealed that 6.5% of patients (19/292) with undetectable EBV DNA and 57.0% of patients (53/93) with detectable EBV DNA during posttreatment follow-up experienced tumor recurrence. Plasma EBV DNA level during posttreatment follow-up is a good marker for predicting distant metastasis, but not locoregional recurrence.

The dynamic changes of EBV DNA in the recurrence and metastasis groups can be summarized by the common rule that the EBV DNA decreased at the end of treatment, approaching 0 copies/mL, although the low concentration was maintained for a short time (approximately 3 months). After 3 months of treatment, the EBV DNA increased gradually until the peak value was reached at the point of clinical diagnosis of metastasis or recurrence. In the recurrence group, EBV DNA increased slowly within 1 year after treatment and increased rapidly after 1 year, with no obvious peak reached. In the metastasis group, EBV DNA began to rise after treatment, which was earlier than that observed in the recurrence group. Although the reason why the patterns of EBV DNA dynamics were different was still undefined, we can make a hypothesis that the patients who suffered recurrence expressed the bigger primary tumor load, which may be more EBV-related than the distant metastatic sites.

The mechanisms underlying the impact of the dynamic changes in EBV DNA load on NPC recurrence and metastasis remain to be clarified, and no risk classification has been effectively demonstrated. Thus, in this study, we stratified the kinetic changes in EBV DNA loads at 0 month, 3 months, 1 year, 2 years, and 3 years after treatment and revealed that different combinations of posttreatment EBV DNA groups may better predict OS, DMFS, LRFS, and PFS in NPC patients. Furthermore, we characterized the patterns of dynamic changes in EBV DNA load in the sustained remission, recurrence, and metastasis groups.

Even if the pretreatment EBV DNA load is higher than the cutoff value of (4000 copies/mL, the prognosis remains good if the fluctuation range of EBV DNA in patients after treatment is lower than the cutoff value. However, the prognosis of patients with EBV DNA loads that continue to exceed the cutoff value after treatment is poor, and the probability of clinical events is high. In such cases, pretreatment EBV DNA load has no prognostic value. Thus, the influence of EBV DNA on survival after treatment is stronger than that before treatment.

In addition, there were significant differences in OS by 12- and 24-month landmark analyses in patients with different EBV DNA load groups. Thus, analysis of this marker should be added to the imaging examination to provide a complete posttreatment follow-up.

Moreover, the present study has several limitations. First, biases due to the retrospective nature of the analyses are unavoidable when the follow-up time is inadequate, and it is a single-center study. Second, not all of the patients in that period have detected the EBV DNA completely and regularly, we have selected patients with complete data. Despite these limitations, the highlights of this study are that it is a large-scale study that evaluated the dynamics of EBV DNA during follow-up and its value for predicting survival. In summary, future prospective, multicenter clinical studies should be warranted to verify the results of this current study.


Epstein-Barr virus DNA kinetics reflects disease progression. Our results showed that in patients with NPC, elevated EBV DNA during follow-up can reflect the possibility of recurrence and metastasis, as well as the unfavorable prognosis. Also, there were significant differences in OS by landmark analysis. These findings indirectly verify the significance of EBV DNA during the follow-up time in NPC. We believe that a better understanding of EBV DNA kinetics would be of paramount importance for the rational use of this new class of tumor marker. Thus, we can use EBV DNA load to intensify the examination or treatment regimens accordingly.


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Dynamic; Epstein-Barr virus DNA; metastasis; nasopharyngeal carcinoma; recurrence; survival

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