The five studies on MGMT in pNET tumor samples found MGMT loss of between 24% and 51% of tumor samples by IHC staining and between 0% and 40% by promoter hypermethylation, revealing discrepancies in methods assessing MGMT expression as well as potential weaknesses in the correlation between MGMT IHC expression and promoter hypermethylation rates.
MGMT promoter hypermethylation was identified in 37.8% of gliomas, but was not present in non-glial tumors, with the exception of one primitive neuroectodermal tumor (PNET).
Drug-resistance genes messenger ribonucleic acid (mRNA) expressions were investigated in drug-resistant human glioma cell lines derived from U87MG and 46 frozen samples of retrospectively examined neuroepithelial tumors (12 low grade neuroepithelial tumors, 16 Grade III gliomas, 11 glioblastomas, and 7 other malignant neuroepithelial tumors such as medulloblastomas and primitive neuroectodermal tumors) by RT-PCR with the specific primers for O6-methylguanine DNA methyltransferase (MGMT), multidrug-resistance gene 1 (MDR1), multidrug-resistance-associated protein (MRP), and glutathione-S-transferase-pi (GST-pi).