Objective: To quantitative analysis of Epstein-Barr virus (EBV) DNA levels in plasma, peripheral blood cells (PBCs) and tumor tissue in nasopharyngeal carcinoma (NPC), to investigate the relationship between EBV-DNA levels and clinical parameters.
Methods: Blood of 150 primary NPC and 49 corresponding tumor tissues, 47 nasopharyngitis tissues and blood of 75 controls were entered this investigation. Plasma and PBCs were isolated for quantitative detection of EBV-DNA by using real-time quantitative PCR (RQ-PCR). The paraffin-embedded tissue sections were conducted to quantitative detection of EBV-DNA, and EBER1 in situ hybridization (ISH) for calculating the percentage of positive cells on the tissue section.
Results: Plasma EBV-DNA levels and detecting rate in NPC before treatment (median 82 500 copies/ml, 92%) were significantly higher than that in NPC after treatment (median 0 copy/ml, 19%) and in controls (median 0 copy/ml, 12%) (P < 0.05), whereas there was no significant difference between NPC after treatment and controls (P > 0.05). There was no significant difference of PBCs EBV-DNA load and detecting rate in NPC before (0 copy/actin, 24%) and after treatment (0 copy/actin, 14%), as well as in controls (0 copy/actin, 16%) (P > 0.05). Plasma EBV-DNA level was not correlated to PBCs EBV-DNA load in NPC before (P = 0.92) and after treatment (P = 0.27), and controls (P = 0.74). EBV-DNA level (27.8 copies/actin) in NPC tumor tissues was significantly higher than that in nasopharyngitis (0 copy/actin) (P < 0.05), and was positively correlated to the ratio of EBER1 positive cells to total cells on the NPC section. In NPC patients, plasma EBV-DNA level was significantly increased in TNM stage I (2500 copies/ml), II (32 590 copies/ml), III (86 000 copies/ml) and IV (166 200 copies/ml), whereas there was no significantly difference of PBCs EBV-DNA loads in difference stages of NPC.
Conclusion: Plasma EBV-DNA level is a more sensitive and reliable biomarker than PBCs EBV-DNA loads for reflection the tumor volumes in NPC patients. Plasma EBV-DNA detection will improve TNM staging in NPC clinical practice on molecular level.