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Quantitative Analysis of the Transrenal Excretion of Circulating EBV DNA in Nasopharyngeal Carcinoma Patients

Authors' Affiliations: ¹ State Key Laboratory in Oncology in South China, Sir Y.K. Pao Centre for Cancer, Departments of ² Chemical Pathology and ³ Clinical Oncology, and ⁴ Li Ka Shing Institute of Health Sciences, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong Special Administrative Region, China

Requests for reprints: Y.M. Dennis Lo, Department of Chemical Pathology, Prince of Wales Hospital, Room 38023, 1/F, Clinical Science Building, 30-32 Ngan Shing Street, Shatin, New Territories, Hong Kong SAR. Phone: 852-2632-2963; Fax: 852-2636-5090; E-mail: loym{at}cuhk.edu.hk.

Purpose: The existence of transrenal clearance of circulating cell-free DNA is controversial. In this study, we used NPC as a model to investigate if circulating EBV DNA can be excreted into urine and to quantify the contribution of renal excretion to the clearance of plasma EBV DNA.

Experimental Design: Quantitative analysis of urine EBV DNA was done for 74 NPC patients using real-time PCR with two different amplicon sizes. The urine concentration of EBV DNA was expressed as copies per millimole of creatinine (copies/mmol Cr) to minimize the effects of interindividual variations in hydration status.

Results: EBV DNA was detectable in the urine of 56% NPC patients using a 59-bp real-time PCR assay. The median urine EBV DNA concentrations measured by the 59- and 76-bp assays were 7,040 and 290 copies/mmol Cr, respectively. Patients with detectable urine EBV DNA had significantly higher plasma concentrations, with a positive correlation between the plasma and urine concentrations of EBV DNA. The fraction of plasma EBV DNA excreted into the urine was 0.0026% of that for creatinine.

Conclusions: We have shown that circulating EBV DNA can be excreted transrenally into urine in NPC patient and the fraction of excretion is negatively associated with the size of the DNA molecules. Because there is a positive correlation between plasma and urine EBV DNA concentration, urine EBV DNA analysis may potentially be applicable as an ultra-noninvasive test for the monitoring and prognostication of NPC patients.