It has been demonstrated that NPCs are associated with EBV DNA infection as the virus infects the epithelial cells promoting the activation of proliferation signalling [37
]. Tumour cells release EBV DNA during treatment, and plasma EBV DNA levels correlate with tumour volume and TNM stage [27
]. Quantitative real-time PCR can detect circulating EBV DNA, and the concentration of short cell-free EBV DNA fragments can predict recurrence and survival. It has been shown that almost all NPC patients have variable pre-treatment EBV DNA copy numbers, and that the highest values correlate with a poor prognosis [41
]. In the case of a CR, pre-treatment levels become undetectable after RT or CRT, whereas some patients with a PR, stable disease or progression tend to maintain high EBV DNA levels. It has been reported that patients receiving standard CRT can be stratified into subgroups on the basis of their pre- and post-treatment EBV DNA levels. Five-year OS and 5-year relapse-free survival are significantly better in the groups with low or high pre-treatment and undetectable post-treatment levels than in those with still detectable levels at the end of treatment [41
In our study, 97% of the patients had pre-treatment levels of >350 copies/mL that significantly correlated with tumour stage (lower values in stage IIb than stages III-IV). According to Leung et al.
] high pre-treatment concentrations during early-stage NPCs are associated with the risk of distant metastases, and Lin et al.
] found that pre-treatment plasma EBV DNA concentrations were lower in patients with local recurrences than in those with distant metastases (1,311 vs
4,253 copies/mL) even if the difference was not statistically significant (p
0.37). They also described 10 patients (10.1%) with detectable EBV DNA levels one week after completing RT, seven of whom experienced a distant relapse, which reflects the importance of undetectable plasma EBV DNA levels in maintaining a disease-free state.
Hou et al.
] found that both pre- and post-treatment EBV DNA concentrations were significantly higher in their patients with distant metastases than in those with long-term disease remission or local relapse. However, in this retrospective study, the post-treatment level was more important than the pre-treatment level in predicting metastases and survival. The same conclusion applies to the study of Chan et al.
], who found that a post-treatment level of >500 copies/mL in patients treated with RT significantly correlated with the poorest outcome, suggesting that this subgroup of patients should be treated more aggressively; on the contrary, levels of <500 copies/mL were associated with a better prognosis.
During the follow-up period in endemic countries, loco-regional recurrence or metastatic disease may be heralded by an increase in plasma EBV DNA levels, which can therefore be considered a useful marker for monitoring NPC patients. In a recent study, Wang et al.
found that 36 out of 245 NPC patients (14.7%) had abnormal plasma EBV DNA levels that accurately predicted all of the NPC recurrences, and no disease was found in five patients with clinical signs of recurrence who were negative for EBV DNA. A PET scan helped in identifying the recurring lesions with a sensitivity, specificity and visual accuracy of respectively 81.8%, 77.1%, and 79.2% [43
In our study on a cohort of patients of Italian origin, we observed three cases of metastatic spread that correlated with very high plasma EBV DNA levels, which must be attributed to an enormous load of tumour cells releasing the virus in blood while replicating. We also found that pre-treatment EBV DNA copy numbers significantly correlate with initial stage (stage IIb vs stage III-IV) and PFS at univariate analysis. Furthermore, the quantification of plasma EBV DNA levels proved to be extremely specific in detecting loco-regional or distant recurrences as none of the disease-free patients showed an increase. Among the relapsing patients, all three with disseminated disease were easily detected by their high EBV DNA loads, whereas the load increased to >350 copies/mL in only two of the four patients with loco-regional recurrences, thus confirming that assaying EBV DNA is less reliable in the case of a limited volume relapse.
It has recently been shown that plasma EBV DNA clearance rates have predictive and prognostic value during the first month of palliative chemotherapy in patients with metastases [44
]. However, the study involved a small number of patients (34 treated with old chemotherapeutic drugs), and the unusually high response rate (41.2% CR) and unusually long OS (median 28
months), which have never reported elsewhere [45
], suggest there may have been a selection bias. Furthermore, the need to analyse multiple plasma samples limits the usefulness of this method in clinical practice.
In a larger cohort of patients receiving chemotherapy for metastatic disease, monitoring EBV DNA levels proved to be useful in predicting which patients would survive longer (i.e. those with low pre-treatment and undetectable post-treatment levels) [47
], which is in line with our experience as some of our long-term survivors maintained low EBV DNA copy numbers years after the end of chemotherapy (data not shown).