Background: Circulating EBVDNA is an important biomarker for ENKTL, which is not just from tumor cells. Tumor cell derived EBVDNA is usually CpG methylated, so detection of methylated EBVDNA may improve its accuracy as a tumor biomarker. Aim: To explore the prognostic value of circulating cell free methylated EBVDNA in 43 newly diagnosed ENKTL patients compared with matched EBVDNA from plasma and whole blood samples. Methods: Enrich CpGmethylated EBVDNA from plasma and then calculate the methylation index (copies of plasma methylated EBVDNA divided by copies of plasma EBVDNA). Results: Among the 43 patients, 32 patients (74.4%) were whole blood EBVDNA positive while 30 patients (69.8%) were plasma EBVDNA positive at diagnosis. However, only 12 patients (27.9%) were methylated EBVDNA positive at diagnosis. Furthermore, the high methylation index was associated with high burdens, and the low methylation index was associated with better treatment response. According to the status of EBVDNA, patients were divided into 3 groups: group A: plasma EBVDNA positive + methylated EBVDNA positive, group B: plasma EBVDNA positive + methylated EBVDNA negative group, group C: plasma EBVDNA negative + methylated EBVDNA negative group. The group A had the shortest overall survival and progression free survival (P< 0.001), and there was no statistically significant difference between the group B and C. The area under curve of methylated EBVDNA (0.8513) was larger than circulating EBVDNA (whole blood: 0.6833, plasma: 0.6615) and the area under curve of PINK E (0.8897) was larger than PINKCpGE (0.9333). Conclusion: Compared to circulating EBVDNA, circulating cell free methylated EBVDNA is better.
