Reply to profiling of Epstein‐Barr virus‐encoded microRNAs in nasopharyngeal carcinoma reveals potential biomarkers and oncomirs

Abstract

Consistent with our findings, Gourzones et al also detected the distinct presence of Epstein-Barr virus microRNA BART7 (ebv-miR-BART7) in EBV-infected patients with NPC relative to their non-NPC cohorts.1 This further substantiates the possibility of EBV microRNAs, particularly ebv-miR-BART7, as blood-based biomarkers for NPC. Although both studies omitted the preamplification step,2 the discrepancy noted by Gourzones et al in the levels of ebv-miR-BART7 between our non-NPC samples may not necessarily be significant. Assuming that microRNAs are present at comparable levels in serum and plasma,3 variations in quantification also may be caused by technical parameters, such as the choice of endogenous control. Gourzones et al determined the levels of ebv-miR-BART7 using hsa-miR-146a as an endogenous control,1 whereas we used mean spiked-in exogenous microRNAs (cel-miR-39, cel-miR-54, and cel-miR-238) and a standard curve of known ebv-miR-BART7 copies.4 Because no study to date has reported the use of hsa-miR-146a as a serum control, we did not test whether our samples would yield similar results under the same conditions. The slightly higher levels of ebv-miR-BART7 discovered in the non-NPC plasma also may be caused by differences in ethnic origin. However, a more comprehensive study is required to test whether normal EBV carriers of non-Southern Chinese descent truly carry more ebv-miR-BART7. Gourzones et al also suggested the use of serum over plasma to improve specificity. Because we were unable to perform a direct comparison, we have insufficient evidence to support the use of one over the other. Existing studies also reveal conflicting results. Although Kroh et al reported that microRNAs are present at comparable levels in both sample types,2 McDonald et al suggested otherwise. The latter group also highlighted the profound effects of preanalytical and analytical parameters on assay imprecision.5 Although we have yet to fine tune existing methods, we believe that assay variations may be minimized by selecting candidate microRNAs under more stringent criteria (eg, high fold change) irrespective of sample type. Alissa Michelle Go Wong BSc*, Janice Wing Hang Tsang MBBS*, Xin-Yuan Guan PhD*, * Department of Clinical Oncology, The University of Hong Kong, Pokfulam, Hong Kong; China.