MGMT and neoplasm: It involves several pathways responsible for development of the tumor cell tolerance to the methylating agents such as increased O-6-methylguanine-DNA methyltransferase (MGMT) expression, impairment of the post-replication mismatch repair system (MMR), or the base excision repair (BER) pathways induced by genetic and epigenetic changes, and resistance to apoptosis due to the reduced Bax (pro-apoptotic protein) level and increased Bcl-2 (anti-apoptotic protein) content [7,8].