26707 MGMT Promoter Methylation Analysis (MGMTD)

​When this test is ordered, slide review will always be performed at an additional charge.

​Prognostication of newly diagnosed patients with glioblastoma

Identification of newly diagnosed glioblastoma patients that may derive benefit from alkylating chemotherapy (ie, temozolomide) 

Therapy selection for newly diagnosed glioblastoma in older patients (>60-65 years)​

This assay requires at least 20% tumor nuclei.

Preferred amount of tumor area with sufficient percent tumor nuclei: tissue 144 mm(2) tissue (4 x 6 mm x 6 mm areas)

Minimum amount of tumor area: 36 mm(2) tissue (1 x 6 mm x 6 mm area)

These amounts are cumulative over up to 10 unstained slides and must have adequate percent tumor nuclei.

Tissue fixation: formalin-fixed paraffin-embedded (FFPE), non-decalcified

Necessary Information:  A pathology report (final or preliminary), containing the following information, is required and must accompany specimen for testing to be performed:

1. Patient name 

2. Block number-must be on all blocks, slides, and paperwork (can be handwritten on the paperwork)

3. Tissue collection date     

4. Source of the tissue

Specimens that have been decalcified (all methods)

Specimens that have not been formalin-fixed, paraffin-embedded

Extracted nucleic acid (DNA/RNA)

​Test results should be interpreted in context of clinical findings, tumor sampling, and other laboratory data. If results obtained do not match other clinical or laboratory findings, contact the laboratory for possible interpretation. Misinterpretation of results may occur if the information provided is inaccurate or incomplete. 

Reliable results are dependent on adequate specimen collection and processing. This test has been validated on formalin-fixed, paraffin-embedded tissues; other types of fixatives are discouraged. 

Improper treatment of tissues, such as decalcification, may cause polymerase chain reaction failure. 

Rare polymorphisms exist that could lead to false-negative or false-positive results. 

This test evaluates for the presence of increased levels of methylation of downstream CpG sites 75-80 and 84-87. Analytical validation studies showed that this assay requires at least 25 methylated copies for a positive result. Retrospective clinical validation study of approximately 200 patients with integrated diagnosis of glioblastoma, IDH-wildtype with grade 4 histological features who were treated with standard © Mayo Foundation for Medical Education and Research. All rights reserved. 3 of 3 of care regiment including temozolomide established the cutoff of 6.50% fraction abundance to distinguish two groups of patients with statistically different overall survival rates. Using the combined cutoff of at least 25 methylated copies and 6.50% fraction abundance to define positive for increased promoter methylation ("methylated") status, patients with tumors positive for increased MGMT promoter methylation ("methylated") status have shown improved survival when compared to patients with tumors negative for increased MGMT promoter methylation ("unmethylated") status. 

Negative results do not exclude the possibility that increased levels of methylation may be present but below the cut-offs for this assay due to low tumor purity. This assay requires at least 20% tumor. 

Negative results do not exclude the presence of increased levels of methylation in other CpG sites.​

MGMT promoter methylation status has prognostic and predictive value for patients with glioblastoma.

When this test is orde​red, slide review (Mayo test code SLIRV) will always be performed at an additional charge.

MGMT (O[6]-methylguanine-DNA methyltransferase) encodes a DNA repair enzyme. This enzyme rescues tumor cells from alkylating agent-induced damage and confers tumor resistance to chemotherapy with alkylating agents. Epigenetic silencing of MGMT by increased methylation of CpG sites within the promoter region results in decreased MGMT expression and reduces MGMT-mediated DNA repair of alkylating agent-induced DNA damage in tumor cells, increasing tumor sensitivity and response to alkylating chemotherapy.

 MGMT promoter methylation status is a molecular biomarker for glioblastoma, which is the most frequent malignant primary central nervous system (CNS) adult-type tumor. In newly diagnosed patients with glioblastoma, MGMT promoter "methylated" status indicating increased levels of methylation is an independent favorable prognostic biomarker and a strong predictor of response to alkylating chemotherapy. Current standard of care treatment for glioblastoma patients consists of surgical resection followed by radiotherapy and alkylating chemotherapy with temozolomide. Older patients (>60-65 years) often have decreased tolerance for combined chemoradiation. For this group of patients, MGMT promoter methylation status guides treatment decision between monotherapy with the alkylating agent temozolomide versus radiotherapy alone.

 Glioblastoma was originally defined solely based on histological features. Based on the 2021 World Health Organization (WHO) classification of CNS tumors, the original glioblastoma is now divided in "glioblastoma, IDH-wildtype, CNS WHO grade 4" (most cases) and "astrocytoma, IDH-mutant, CNS WHO grade 4".(1) In isocitrate dehydrogenase (IDH)-mutant diffuse gliomas, MGMT promoter "methylated" status is frequent and strongly associated with the IDH mutation-induced glioma CpG island methylator phenotype (G-CIMP), except for the uncommon infratentorial IDH-mutant astrocytomas. Therefore, the clinical significance of MGMT promoter methylation status in the context of IDH-mutant diffuse gliomas is less firmly established.

 MGMT promoter methylation status may be evaluated by multiple methods, and the testing platform with most prospective clinical trial validation is methylation-specific polymerase chain reaction evaluating downstream CpG sites.

​The interpretation of molecular biomarker analysis includes an overview of the results and the associated diagnostic, prognostic, and therapeutic implications.