Abstract: Objective To detect the methylation of gene O6-methylguanine DNA methyltransferase (MGMT) in peripheral plasma of patients with diffuse large B-cell lymphoma (DLBCL)，and to evaluate the relationship between methylation of MGMT and efficacy of chemotherapy on DLBCL.Methods  Before and after chemotherapy，nestedmethylation specific PCR (nMSP) was performed for detecting methylation of MGMT in plasma from DLBCL patients who were treated with CHOP.Result Methylation of MGMT was found in 63.3% (19/30) of patients with DLBCL.The response rates were 100% (19/19) in patients with methylation of MGMT and 72.7% (8/11) in patients with non-methylation of MGMT，and the difference between two groups was statistically significant (P=0.041).The ratios of resistance to chemotherapy were 10.5% (2/19) in patients with methylation of MGMT and 54.5% (6/11) in patients with non-methylation of MGMT，and the difference between two groups was statistically significant (P=0.028).Conclusion Methylation of MGMT in peripheral plasma of DLBCL patients might be a biomarker of response or resistant to chemotherapy with alkylating agents based regimens.

Key words: Lymphoma, Diffuse large B-cell lymphoma (DLBCL), MGMT gene, DNA methylation, Chemotherapy