Following this repair process, MGMT is irreversibly inactivated and subsequently degraded by the proteasome.[5] It has been reported that in about 50 % of GBM tumours there is active MGMT expression, corresponding to hypomethylation of the MGMT promoter, whereas in the other 50 %, MGMT expression is silenced due to promoter hypermethylation. Here, MGMT is linked to glioblastoma.