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MGMT Immunohistochemical Expression and Promoter Methylation in Human Glioblastoma.

Posted on: 12/21/2007

Appl Immunohistochem Mol Morphol. 2007 Dec 12; [Epub ahead of print]

MGMT Immunohistochemical Expression and Promoter Methylation in Human Glioblastoma.

Rodriguez FJ, Thibodeau SN, Jenkins RB, Schowalter KV, Caron BL, O'neill BP, David James C, Passe S, Slezak J, Giannini C.

Departments of *Laboratory Medicine and Pathology double daggerBiostatistics daggerNeurology, Mayo Clinic, Rochester, MN.

O6-methylguanine-DNA methyltransferase (MGMT) expression has been recently proposed as a useful prognostic and/or predictive marker in glioblastoma patients receiving adjuvant therapy after the surgery. We studied samples from 50 patients with histologically confirmed GBM to evaluate MGMT expression by immunohistochemistry and its relation to promoter methylation status. Genomic DNA was extracted from scrapings of formalin-fixed, paraffin-embedded tissue corresponding to hematoxylin and eosin sections. Using the mouse monoclonal antibody MT3.1, MGMT expression was assessed and scored in tumor cells: (1=negative or limited to <10% positive tumor cells, 2=10% to 50%, 3=>50%). Methylation-specific polymerase chain reaction was performed after bisulfite treatment. Assessment of MGMT expression in neoplastic tissue required careful scrutiny because of its expression in a variety of non-neoplastic cells. MGMT expression was present in tumor cells with a score of 1, 2, and 3, respectively in 36 (72%), 13 (26%), and 1 (2%) cases. Methylation-specific polymerase chain reaction yielded interpretable results in 39 cases (78%). MGMT promoter methylation was detected in 15 cases (38.5%), whereas 24 (61.5%) were unmethylated. Among the methylated samples, 14 (of 15) had a score of 1, and 1 had a score of 3 by immunohistochemistry. Of the 24 unmethylated samples, 18 had a score of 1, and 6 of 2. There was no significant correlation between MGMT expression and methylation, and no significant survival difference was observed between patients whose tumors were negative versus positive for MGMT protein by immunohistochemistry. This study underscores some of the difficulties in applying immunohistochemistry to assess MGMT expression.

PMID: 18091318 [PubMed - as supplied by publisher]

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