Methylguanine-DNA methyltransferase (MGMT)

Last revised by Frank Gaillard on 23 Nov 2021

O6-Methylguanine-DNA methyltransferase (MGMT) is a DNA repair enzyme which is important in predicting the effects of alkylating chemotherapeutic agents (e.g. temozolomide) in the treatment of glioblastomas (GBM).

MGMT methylation is very common in low-grade gliomas (80%) 2 and is almost invariably present in low-grade tumors with IDH mutations 3. In contrast, MGMT methylation is far less common in higher grade gliomas (WHO grade 3 and 4), found in only 35-45% of such tumors 2

Assessment

MGMT methylation can be assessed with numerous techniques and no uniform consensus has been reached in regards to which technique is the most appropriate in clinical practice. Immunohistochemistry, nonquantitative methylation-specific polymerase chain reaction (MSP) and sequencing have all been used. 

Viable (non-necrotic) tissue must be sampled to avoid false-negative results 2

Prognostic impact

High activity of MGMT (i.e. unmethylated) results in reduced efficacy of alkylating agents, and thus is a poor prognostic factor 1,2

On the other hand, when the MGMT promoter is methylated, there is decreased activity of MGMT and thus alkylating agents are more effective. In other words, the identification of methylated-MGMT is a positive prognostic factor 1. It is also predictive of pseudoprogression following Stupp protocol 2.

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