To test whether the levels of (i) EBV copy number, (ii) HOXA2 methylation ratio and (iii) MMP-9 levels are inter-correlated in a given sample, we obtained 3~5 follow-up plasma samples from five treated NPC patients (Fig. 5, designated A~E; N=22), and EBV copy number in the plasma was monitored by q-PCR; and cfDNA was extracted from the samples and methylation specific-high resolution melting (MS-HRM) (Fig. S7 and Table S4) and q-PCR was performed to detect the HOXA2 methylation ratio; and the MMP-9 levels of the plasma samples were detected by the ELISA. The gene discussed is MMP9; the disease is nasopharyngeal carcinoma.