International Journal of Radiation Oncology*Biology*Physics
Clinical investigationHead and neckRelationship between pretreatment level of plasma Epstein-Barr virus DNA, tumor burden, and metabolic activity in advanced nasopharyngeal carcinoma
Introduction
Epstein-Barr virus (EBV) and its gene products are ubiquitous to the nonkeratinizing subtypes of nasopharyngeal carcinoma (NPC) that are endemic to South-East Asia (1). NPC is special among EBV-related malignancies in that a substantial body of literature supports both a pathogenic and prognostic role of EBV in this disease. The clonal nature of NPC-derived EBV DNA suggests that these tumors represent progenies from a single cell that was initially infected with EBV (1). The presence of clonal EBV DNA in preinvasive and invasive lesions of NPC further highlights the contribution of EBV to its early pathogenesis (2). With the discovery of circulating EBV DNA in vivo and its quantitative analysis with real-time polymerase chain reaction (PCR) (3), the idea of an efficient and noninvasive monitoring of NPC is becoming a clinical reality (4). The level of plasma EBV DNA (pEBV DNA) in patients with NPC has been shown to reflect disease stage and activity (4, 5, 6). Moreover, elevated level of pEBV DNA detected at 6 to 8 weeks after radiotherapy (RT) is a powerful prognostic indicator that is independent of disease stage in advanced NPC (7). The basic tenet behind these clinical observations is that circulating EBV DNA originates primarily from the tumor and is released directly into the bloodstream. Given the clinical correlation between disease activity and pEBV DNA (4, 7), it has been postulated that the amount of viral DNA release may be proportional to the host’s tumor load (7). This idea is further given credence by the result of a recent study which reported a linear relationship between the plasma concentrations of tumor-derived nuclear EBV DNA and tumor mass (weight in grams) in a nude mouse model of NPC (8). Whether this association can be observed in the clinical setting requires further evaluation.
18F-fluorodeoxyglucose-positron emission tomographic scanning (18F-FDG-PET) exploits the principle that most cancers have a higher rate of glucose utilization relative to normal tissues. Uptake of the 18F tracer is conventionally expressed as the maximum standardized uptake value (SUVmax), a semiquantitative value that reflects the rate of glycolytic metabolism in tumors (9, 10, 11, 12, 13). In general, tumoral uptake of 18F-FDG is influenced by multiple factors including the blood sugar level, number of viable cells per unit volume (14), tumor vascular supply (e.g., microvessel density), and expression level of intracellular glucose transporter Glut-1 and hexokinase I (15, 16). Other studies have also found a positive correlation between 18F-FDG uptake with histologic markers of tumor proliferation (9, 10, 11, 12, 13). Given the 18F-FDG-avidness of NPC and the established role of PET in the detection of NPC recurrence following RT (17, 18, 19), 18F-FDG-PET imaging thus represents a useful tool for evaluating the relationship between tumor metabolic activity, tumor volume, and the level of pEBV DNA in patients with advanced NPC. In the past, tumor detection and staging in the head and neck region were suboptimal because of a lack of anatomic precision of the PET scan. This often resulted in erroneous upstaging by inclusion of physiologic 18F-FDG uptake in normal tissues. The advent of dual modality PET-CT had corrected this deficiency, resulting in a more accurate measure of the tumor status (20, 21).
The primary objective of this study is to test the hypothesis that circulating level of EBV DNA is related to tumor volume and metabolic activity in advanced NPC. The secondary objective is to investigate if the radiologic volume of a tumor is related to its metabolic activity. The study design involved correlating pretreatment levels of pEBV DNA with magnetic resonance imaging (MRI)–delineated tumor volume and with tumor metabolic activity as indicated by 18F-FDG-uptake on PET scans, in patients with locoregionally advanced NPC who were enrolled in a randomized clinical trial running in parallel to this study.
Section snippets
Patient selection
Patients enrolled in a randomized phase II trial conducted at the Prince of Wales Hospital gave informed consent to this parallel study, which was approved by the institutional Ethics Review Board. This phase II trial randomized patients with undifferentiated NPC to concurrent cisplatin-RT with or without induction chemotherapy with cisplatin-taxotere. All patients had to have nonmetastatic American Joint Committee on Cancer (AJCC) Stage III to IV NPC based on the following staging procedures
Results
A total of 60 patients were enrolled into the main clinical study over a 2-year period (27), of whom 57 patients were eligible for this parallel study. Three patients were excluded because they had pretreatment MRI performed at another hospital and refused a repeat MRI for this study. The majority of accrued patients were males with a median age of 48 years (range, 31 to 70 years) and Stage III NPC (Table 1). A total of 25 patients were subsequently treated with concurrent cisplatin and RT,
Discussion
In this prospectively designed study, pretreatment level of pEBV DNA was found to be independently associated with MRI-delineated total tumor volume (i.e., volume of the primary tumor and regional nodes) among patients with detectable levels of pEBV DNA and advanced undifferentiated NPC. Moreover, MRI-delineated volume of the primary tumor was also independently associated with 18F-FDG uptake at the primary tumor. This result supports our hypothesis that the level of pEBV DNA reflects overall
Conclusion
In conclusion, this study supports the preclinical finding that cell-free pEBV DNA is related to tumor burden in patients with locoregionally advanced undifferentiated NPC who have detectable levels of plasma EBV DNA before treatment. Whether this applies to earlier staged NPC is unclear and requires further validation. Given the association among pEBV DNA, prognosis, and tumor burden, future effort should be focused on how this molecular marker may be effectively incorporated into the
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2020, Radiotherapy and OncologyCitation Excerpt :Many authorshave already proposed that TNM stage is insufficient because of differences in outcomes of patients with the same stage receiving similar treatment [8,9]. Relevant indicators of tumor burden, including PTV and EB-DNA has been proposed as an additional stage indicator in the new revision of the clinical stage [8,10]. In the study of Guo et al. [20], the 5-year OS for NPC patients with PTV <19 vs. ≥19 ml were 97.0% vs. 76.4% (p < 0.05) and the multivariate analysis indicated PTV was an independent prognostic factor.